SICMINAKS IN NF.UKOI.O(;Y-V01,UME:
I I , N O . 4 I)BCb,':',MHEK 1991
HISTORICAL NOTES
Writing for Lefty
1 a m a lefty and, if T/io N P ~Er~gl(md J J o ~ ~ r t i(4' d \\.it11 which I have, nioments befi11.e and, as is usual f i ~ r ~LZoclic~in~ is right (correct, that is), I have about a rile, using my left hand to do it, snipped the thread with year left (on earth, that is).' I have, therefore, tle- which I had, also lefthatidedly, sewn the button to the cided to write about rnyself (from now o n , please pay no attention to the wordplay that this discussion may call fi)rth) with regard to my handedness, although the subject is only loosely linked with clotting disorders, the sul?ject of' this issue of' Seminars, the connection I)eirig the intiisputable fjct that the worst thing a blood clot can d o is rob someone of his communicative capacities. (For me, the gold stantlard of' cor~imunicationis the written word.) I want to explore a little the specializations of the hen~isphercs, their ability to conin~unicatewith each other and the world, and suggestions that no re than one integrated personality may have an anatomically cleli~nited1oc:us within a normal person's c r a n i ~ ~ r n . First, let me tell you e r ~ o u g habut myself and my unique experience a f e w years ago to show you what made me put this essay together. T h e n I shall draw o n the perspectives of a neurologist, a neuroscientist, a n d a philosopher to try to make sense out of' what happened to me. (When I say, " a neurologist," a n d so forth, I mean, literally, one of each; 1 pick my way through a subject like a boy crossing a creek o n steppingstones, in the belief' thac the fewer rny hops the smaller my chance of getting into d e e p water.) ,\I? ~ ' ( I s P : It is e;11.1\.~not.tiing.I have just finished scwing ;I button ol~tothe shirt I \cant to wear that day. I c-I-ossh e livingrooni c-;u.t.yingin 111); right hand a spool of'white thread ; ~ n di n n l ) left hatid the pitir of scissol.s
collal- of the shirt. I am pleased at having successfully completed, so soon after waking, my small but somewhat rtnuccustolried task. I approxh the table frorn the left and, with my right hand, the one holding the spool, I pull open a small drawer. I t was my intention as I approached the table to dcposit both spool and scisso~-sinto the drawer. I drop in the spool of thread, push the drawer shut with my I-ight harid. As I ti1111 from the table, in my left field of vision I catch 21 glimpse of' the scissors, still grasped in the fingers of my left hand. At the smmc instant, 1 hear a distinct, and distinctivc, voice cxclaim, with emotion, "Stupid!": I know at ot~c-cwhere that voice is corning frorn, and I have a new illsight into the workings or my t)rain.
7 ' 1 1 ~ N(~urologkt.It was o u r Founding Editor, Robert Joynt, who first got me to wondering about which hemisphere I riormally speak with. H e would reawaken my interest yearly by remarking to the medical students, during his annual lecture o n aphasia (while I, their teacher, sat among them), "It will be interesting to see, when Dr. Goldblatt gets his stroke, whether o r not he becomes aphasic." With the spontaneity that rehearsal befbre a changing audience permits, I would retor-t, "It will be interesting to see if' you're still around when I get it." 7'lw N P U T O S C Z PRobert ~ / ~ Z YDoty ~ . is the premier neuroscientist at the Uriivcrsity of Rochester (and, by extension, in the world). H e recently entered a vigorous retirement that gave him enough time to have a chat with me about My ( h e and the duality
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David Goldhlutt, M.D.
of' brain organization. H e has thought about this kind of thing a long time-Sperry was a guest advisor on his doctoral committee. We talked about the monkey experiments in which he stimulated the striate cortex o n o n e side when the corpus callosurn was intact, training one hemisphere: when he then cut the corpus callosum, with the ingenious snare that he devisecl, and isolated the other hemisphere, it did not know the answer that the previously stimulated hemisphere could give.' If one hemisphere is trained with a visual stimulus through the visual pathway, when the optic chiasm has fir-st been split to confine the input to one hemisphere, the other side does learn the answer. ' I h e idea o f a unilateral engram would make sense, Doty said to me, as a means of doubling the mnemonic capacity of the brain, as he previously hypotl~esized,:~ "but if the system doesn't work that way, too bad: great theory but so what. We try to weasel out by suggesting that if the thought, the language learning, is originating in the cortex, that might make a difference. When things a r e coming in through the normal sensory channels, both hemispheres have access to t h e information. 'The big hooker in all of' the tachistoscopic experiments in intact man is that if you deliver a tachistoscopic stimulus to one hemisphere it may be in that hemisphere for 5 to 10 milliseconds. T h e n it gets over to the other hemisphere a n d so it's rattling around all over the place. What kind of laterality experiment is that?" I was intrigued by the idea that thoughts might be like the electrical stimuli, keeping their own company in a piece of cortex o r at least o n one side of'the brain a n d not the other. A second idea of use to me corlcerned the lirnitations of the corpus callosum, even when it is doing its best. To approach that, consider it at its worst. when it has been divided by a neurosurgecn. Iloty, in one of' his essay^,^ reviews an observation of' 'IFevarthen on a split-brain patient that "strikingly illustrates the power of'. . . brainstem switching of' visual consciousness." 'I'lle patie~ltwas to use her left hand to mark a white object o n a black cloth in the right visual field. However, she reported that the instant she began to move her left hand toward this object, it disappeared! In other words, as her attention shifted to her right hemisphere fi)r movement of the left hand, visual attention was also trauskrred from the right to the left visual half-field; without the corpus callosum and the anterior cornrnissure the visual world was ueatly partitioned between the right anti left hemispheres and which hemisphere "saw" dqmided on which was queried.' As for the corpus callosum at its best, and its limitations, that is a topic of present interest to Doty. H e has collaborated in a morphometrically 420
V0I.UME 11. NUMBER 4 I~I:'CEI\IBI:II I991
ljasecl postulate that requires intrahernispheric integration of' complex tasks of information processing, simply because repeated transcallosal passes must be too slow to do the job, given the conducting capacity of' the system, the spectrum of' conduction velocities availalde, and the distances involved. "If' the, presunlably overlapping, neural assemblies needed to handle overlapping tasks are clustered together, this would lead to hemispheric specialization. T h e prediction follows that the large brains of mammals such as elephants and cetaceans will also manifest a high degree of' hemispheric specialization."' Because of' the emotional character of the exclarnation I heard in my head, I was greatly interested, also, in Doty's thoughts on the subject of emotion. H e has reviewed the considerable clinical intormation concerning the dif'ftring effects on mood a n d behavior of lesions in the left versus the right hemisphere.“^" [I'lhe evidence is rather good that the two heniisp11erestno1-mally have different emotional outlooks, probably because of the unilaterality of the first-order co~mectionsfro111the aniygdala. How this difftrence in emotional tone of the two hemispheres is accomn~odated in normal individuals is as obscure as any other interchange between them. A well-documented case exists, however, in which the subject, initially troubled by ;~brupt,spontaneous emotional transitions, learned t o contl-ol these rnoods; laboratory findings n~uchlater revealed that her control was achieved by switching clominance f'rom one to the other hemisphere. [See Doty' f i r references omitted here.]
I n his characteristically meticulous way, Doty has assembled evidence for a startling idea: because there is "a central role for the amygdala in the expression, a n d probably the experience, of' emotion in man a n d animals . . . [and because] the amygdala shares with the hippocampus in primates a sparsity of interhemispheric connections, [should] 'sharing' [between the hemispheres] be impaired, the anatomical possibility also exists fbr each hemisphere to pursue a semi-independent emotional life!"" It is his belief that perturbation in the "dynamic equilibrium" of the two hemispheres, achieved normally through "neural competition," underlies schizophrenia. Abnorniality of featul-es reflecting interhemispheric processes is cornmou in schizophrenic patients; and the 'first-rank' symptoms o f delusions or hallucinations are prototypical of' what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is ti)cussed primal-ily through, the raphC serotonergic systern, that plays such a fundamental role iu consciousness, in dreaming, iu response to psyctlotonlirnetic drugs, and
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SEMINAKS IN NEUKOI,O(;Y
12ec;1usethis is not true, we cannot cxplailt the unity of a person's life by claiming that the expel-iericcs in this lifc are all had by this person. We can explain this unity only b y describing the various relations that hold between these diflkrcnt experiences, a n d their rclatiorls to a particular brain. We could therefore describe a pet.-
sott's life i n a n impersonal way, this person exists.
which does not claim tha
0 1 1 this Keductionis~View, persons d o exist. B U I they exist only in the u x y in which nations exist. Pet-son'are not, ;is we mistakenly believe, fu~idam~r~tcd. This vieu is in this sense more imperwn;~l.~~"'~
If' o u r identity is not what matters, what is i~ that does matter? "What matters," Parl'it concludes, i c -iohc~tmrtkrs us prrwns." What niatters i:. "psychological continuity antilor connectedness." H e ~vantsus to 11c clear that ' h o s t of us slioiildl change our view about the nature of' persons, and personal identity over time. T h e truth is here ver) ciif'f'erent from what niost of us belicve."'P'"' Hi:) truth about the "state of awareness" that exists within a disconnected hernispliere does offer a wa) to think about the paradox of the divided brain. but the reader who wishes to grasp it must turn to1 t to understancl him I'arfit's writings. I d o ~ i o claim well enough to epitomize his thought, and t h a t ' ~ not fair to a philosopher anyhow. My Ex/hwtion. 1 am, as I said, left-handed. My father and his sister (his only sibling) as well as both his parents were left-handed. I can f ~ i r l y claim that I came by my handedness naturally. although those who blame siriistrality on birth trauma have an argument in my case, since I experienced consideral~le fetal distress during my birth and was a "version a n d footling," as I have previously described. ' 1 have, however., been acculturated as a righthander for writing antl eating. Switching me to my right hand Ibr writing was acconiplished bv my parerits when 1 was a preschooler. Dad wrote righthanded, but that was because he had been fi)rced into it in school: he did not want to treat his first child the same way, but h e recognized the conve11ie11c:eof writing right-handed. So Mom and Dad ~tsetireward instead of' punishment to alter the behavior of their little boy: I had a blackboard. and when I attempted to draw o r to "write" o n it with chalk, left-handed, they would say, "'That's very nice, Ihvey; now show us what you can d o with your o t l ~ e rhand." When I then tried my right, ~ l i c ywould ~ i ~ u r m ua11 r approving "Ooh!" and praise my work. 'l'he flattery succeeded and, by the time I entered school, I was writing and drawing with my right hand, but I retained left-handedness for everything else arid was left-footed a n d left-eyed. I still play sports and d o home repairs left-handed antl I cut that way with scissors, despite the discomfbrt that the usual handles create. I was in my teens before I went along with the idea of holding a n eating utensil in my right hand, hilt it was a compromise, making me a two-fisted eater (knife in left
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111-obablyin tno\zcmcnt,m d even the tt-ophic state o f the tteocot-[ex.' 7 . h ~f ' f ~ i l ~ ~ oTphle~ stock ~ ~ . in trade of presentday philosophers seems to be problem cases, science-fictionlike situations in which brains are divided between diff'erent bodies, o r minds are fused, o r in which replicas of persons are sent to other planets, all in the interest of illuminatiiig questions of personal identity. I n an uninitiated person like me, these exarnples elicit two kinds of response: willingness to follow the analysis fin- the sake of the legitimacy of the question, o r ridicule because I have enough things to worry about without the silliness of half-brain transplants a n d of illstantaneous space travel-the odd kind that d s o leaves the traveler where he was to start with! Oxfbrcl philosopher Derek ParEit argues, not unpersuasively to a neurologist, that in even the extreme o r limiting case of' organ transplanlation-his brain into another body-"it may seem that I am here the dead donor. But I am really still the recipient, arid the ~ u r v i v o r . "I'art'it's ~ thinking is also accessible to the rieurologist when he turns to neuroanatomy a n d the split-brain expel-inients. Almost as quickly, however, h e turns the actual experinients into t h o u g h t - e x p e r i ~ s by , positing, for example, that h e can, by activating a switch attached to his eycbr-ow, disconnect the "exactly-siniilar-" hemispheres of' his brain. (He quite understantis that his brain is in that respect atypical; h e is making a n assurnptiori to develop his argument.) When we imagine the possibility that, in a briefly divided brain, two strearns of consciousness may How tfiroi~ghparallel channels and then, at the flick of a switch, reunite like the parallel streams o f a river flowing past an island, we must consider- the possibility that, during the time of separatioti, two persons have come into being within a single body. 'l'hat is 11y no means the only possib_ility.You will need to read him to get the idea of what he calls My Division: "Call one of the resulting people Lrlftj. I might ask, 'Are I& and Dorek Parfit names of' one and the same person?"' he writes, and goes on from Central to Parfit's thought is the idea that our k h t i t y i~snot wlm&mutt~rs.*-'~ H e powerfully contests the view of' 1)escartes and of' many others concerning an Ego, a person as a thinker of thoughts o r subject of experiences. As a supporter of the Keductionist view, h e disbelieves that we a w such "entities":
'
42 1
resides in the right hernisphere of' those persons who speak primarily with the left hernispherc, arid that left-hantlers often have language capacity that is clistl-ibuted more evently between the herriispheres than right-1laritle1-s do."' It is no surprise that my r-ight brain easily had the capability of'calling me stupid. Dr. 1)oty's ot)scrvations, cited before, make me believe that, at a tirrie shortly after waking, when the alerting o r energizing influence of the brainstern is not fully operatio~ial,when I shifted my attention into my r-ight hemisphere hy catching sight of the scissors in niy left hand, I also "lighted up" the language capability of that hemisphere, which escaped the suppressive influence of the left and permitted the exclamation "Stupitl!" to be voiced internally. T h e analogy is with having enough power coming into the house through the basement to light only one of the two upstairs bedrooms at any one tirne. This is a different idea froni that of Parfit's eyebrow switch, which tlisconnects the hemispheres horizontally; but vulnerability of' the fi)rel)~-ainconiniissures to states of' impaired alertness, undue fatigue, intoxication, and the like cannot he excluded as a cause of physiologic cleconnection. If we accept that there are times when the alien voice of the r-ight hemisphere speaks in o u r heads, the reniaining question is, "How do we hear it?" 'I'he possible explanations are: ( 1 ) we hear it in the left brain, (2) we hear it in the right, and (:3) we hear it in t ~ o t h .It would not be fair t o add the brainstem as a site of recognition. We are, af'ter all, neurologists, not philosophers, and the premisses of our syllogisms have their limits. ' I h e "head ganglion" of the subcortical emotional system, the arnygdala, however, has a private relationship with its o w n hemisphere, as Doty points out, ant1 has the capability of' giving emotional tone and feeling to an utterance; to that extent, the subcortical system ( o n one side) may well be involved. My opinion allout My Case is that I heard the voice in my right brain-that, at that nlonicnt, tny consciousness was 1.ig1lt-heniisphcl-icin its locus. I cannot, after reading in Par-fit, clai~nthat I 7 m . s . briefly, a pcrsori whose right hemisphere was his brain, but at least that's where the action was. What I believe happens niuc:h niore often is that my right 1)rai11controls my left and makes it d o things it doesn't want to do. Onc last example is a piece of writing, called hly Experiment, with which 1 close this too-long essay. It has the antiintellectual quality I have been trying, all through this essay, to avoid a n d a flippancy o f t o n e that undermines what I have 1)eeli working so hard to get ;icross. I know very little about my right brain, of
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hand, spoon o r fork in right). A n d I can do syrnmetrical things two-handed, such as drawing a cross-section of the spinal cord o r the nledulla on the blackboard fbr my students, who seem to think they have "seen something amazing" (to use Auden's phrase), whereas for me it's easy. I believe that I speak with my left hemisphere. I can't use the way I hold a pencil as a way tojudge that, since I d o not hold it in my preferred l ~ a n d , if that is what I may call my left hand. I am a "pusher," not a "hooker," but I don't even know how I would have written lef't-handed without the model of my right to follow. Normal writing posture in both right-handers anti left-handers has been correlated with contralateral hemispheric specialization thr language and ipsilateral visuospatial superiority.".'" A n inverted writing posture indicates ip.silutrru1 language specialization arid contrcdnt~rnlspecialization for "n~eritalimagery and the understanding of spatial relationships": a reversed situation." Whether, i r i a left-hander who writes with the left hand, that hand is controlled by the right hemisphere after receiving its instructions transcallosally froni the left (if, as in the ma,jority of such cases, the left is the speech hernisphere) o r whether the left hand is contl-olled ipsilaterally for writing is not known.'" How can I infer that my left is my speech hernisphere? (This is what 1)r. Joynt first r i d e rile seriously consider.) I don't like to think about it, but I have to: my dad and his mother both had strokes, late in life, that affected the left side of the body. Dad's was embolic, in the territories of the right anterior anti rriiddle cerebral arteries. For a few days, his speech was slurred and he repeated what he had just said, probably to be sure I understood him (or maybe it was palilalia). For a longer time, his speech lacked prosody. Neither he nor his mother was aphasic. Knowing that about those left-handed per-sons with whom I am genetically linked is enough to convince me that I, too, speak with my left brain. Like many people, I talk to nlysrlf; arid I "hear" the words I read o r write. It slows me clown, but it is how my brain works. (Are you that way, also? If' so, you have my sympathy.) But there is all the difterence in the world between those usual, internally "voiced" thougl~ts(which are, I believe, of left hemispheric origin) anti the z~oiwthat once, and, thus far, once only, spoke to me and called me stupid. -1hat was, as I sensed at once, ttu~z w i r ~(4 my right hemisf)herr, speaking to itself loudly enough for- me to hear it. My recognition of "physiologic deconnectiori" was born. We know from the effect of left-brain strokes and hernispherectorny that interjectional speech
I n summary, let m e I-eiterate that what we have assun1c.d to be a real experiment by a real neuroscientist is only what has been relkrrecl to as a C;edankenexperiment, f'rom the ( k r r n a n word h r " l ' h a r ~ k you!" 'l'he good fortune of this is a p p a r e n t ,just when we realize that, if' the expel-inlent Ilad been a real o n e a n d il', f i ~ r thel-ac.c.epting the prerniss that all pl~ilosopherslook m d act alike-we wo~rlclhave n o way of krlowing which 01' them had undergone the surgery, we \vould b r left wit11 the ambiguous a n d unsatisfactory situation that, in any personal encounter with a philosopher, we might actually be speaking with philosopher A, who had t h e I x t i n of' a Brussels sprout, o r philosopher B, who had n o brairl at all.
,\.II. I:',x~errrtr~t1/. 11mgi11ethe lollowing cxpcriment: neul-oscicntist has in his laborato~-ytwo philosophers. A l t l ~ o r ~ geach h espouses ;I tlif'lkt.rnt school of' p l d o s o p h y (each is, illdeed. t h e only enrollee in each of those schools. where tuition is nierely recommentlcd a n d attentl;uicc is taken 1,ut not in ;I spirit o f hopefulness), h e y t~evet-thlcsslook identical to each other. (Iktails of this a r e u ~ l i r n p o r t ; ~ nmake t: some of their ftatut-es curly hair. a n d wil-e-ri~nmetlgl;~sses.I f you need this, ; ~ d da c.ol'1i.c (-1111 that has rlcvct- beet1 washed.) Now i ~ x ~ g i t lf e~ ~ r t h ethat r this neuroscientist has Besides my obvious debt to Bob Doty, I owe thanks just t.eturt~ed f'~.om;I I-wcck trip to a dista~lt galaxy where he has :I time-sh;tre ;mtl that, durirlg the I-eturn, to philosopher ,Jeltiey Spike, of the Division of Medical I I u t ~ ~ a n i t i cUniver-sity s, of' Kochester School of' Medicine Ire Ilas lef't hr.\ glasses, which m.c tinted t~ifocals,in the ;ird 1)entistl-y. 1 should also acknowledge the extetlt of sp;~ccship. 111) ignorance of'the subjects discussetl, but 1 believe that Notwithstanding, t h e neut-oscie~itistis hellbent o n 1 have alrcittly gotten that across in the text. his experiment, which irivolves retnoving the 11r;lins of' the philosophers. by means of'a recently perftcted technique in which Heineke11 beer is 11sec1as a perf'usate d u r ing t h e p~.vcedure,anti replacing them with ;I lest). vege t h l c . For this, the ~ ~ c u ~ - o s c i e nhxs t i s t a limited nunil)er REFERENCES of choices-the ~ r s l ~ a l liicceptrd ) urnhe her is live-sitice the intuitively obvious choices, caulitlo\vet. and cabbage, I . Ilalperti 1)F. (;oren S. H;tntlcclnc\s antl lilc span (Icttcr-). arc, pr;~ctically speaking, unavail;~lde becar~scof' their N Errgl ,I hletl 1W1 :324:01)8 large size. Since thcse five choices have I ~ e c ntlisc.ussetl at T lloty KLV. Klcctl-icalstimulatiorr of'thc brain in l x l ~ i~)ral a~ length previously (see my essay in Self a n d Shelf: O I I ~ contest. Atinu Krv 1's)cllol lCW);20:280-32O metaphysical 1a1-tier) let us settle o n one: the B r ~ ~ s s e l s 3. l h t y K\V, Ncgr-io N, Yarnag;~K . The u~rilatcralctrgt-am. spt-out. A t t ; ~Ncut-ohiol I
I I , N O . 4 I)BCb,':',MHEK 1991
HISTORICAL NOTES
Writing for Lefty
1 a m a lefty and, if T/io N P ~Er~gl(md J J o ~ ~ r t i(4' d \\.it11 which I have, nioments befi11.e and, as is usual f i ~ r ~LZoclic~in~ is right (correct, that is), I have about a rile, using my left hand to do it, snipped the thread with year left (on earth, that is).' I have, therefore, tle- which I had, also lefthatidedly, sewn the button to the cided to write about rnyself (from now o n , please pay no attention to the wordplay that this discussion may call fi)rth) with regard to my handedness, although the subject is only loosely linked with clotting disorders, the sul?ject of' this issue of' Seminars, the connection I)eirig the intiisputable fjct that the worst thing a blood clot can d o is rob someone of his communicative capacities. (For me, the gold stantlard of' cor~imunicationis the written word.) I want to explore a little the specializations of the hen~isphercs, their ability to conin~unicatewith each other and the world, and suggestions that no re than one integrated personality may have an anatomically cleli~nited1oc:us within a normal person's c r a n i ~ ~ r n . First, let me tell you e r ~ o u g habut myself and my unique experience a f e w years ago to show you what made me put this essay together. T h e n I shall draw o n the perspectives of a neurologist, a neuroscientist, a n d a philosopher to try to make sense out of' what happened to me. (When I say, " a neurologist," a n d so forth, I mean, literally, one of each; 1 pick my way through a subject like a boy crossing a creek o n steppingstones, in the belief' thac the fewer rny hops the smaller my chance of getting into d e e p water.) ,\I? ~ ' ( I s P : It is e;11.1\.~not.tiing.I have just finished scwing ;I button ol~tothe shirt I \cant to wear that day. I c-I-ossh e livingrooni c-;u.t.yingin 111); right hand a spool of'white thread ; ~ n di n n l ) left hatid the pitir of scissol.s
collal- of the shirt. I am pleased at having successfully completed, so soon after waking, my small but somewhat rtnuccustolried task. I approxh the table frorn the left and, with my right hand, the one holding the spool, I pull open a small drawer. I t was my intention as I approached the table to dcposit both spool and scisso~-sinto the drawer. I drop in the spool of thread, push the drawer shut with my I-ight harid. As I ti1111 from the table, in my left field of vision I catch 21 glimpse of' the scissors, still grasped in the fingers of my left hand. At the smmc instant, 1 hear a distinct, and distinctivc, voice cxclaim, with emotion, "Stupid!": I know at ot~c-cwhere that voice is corning frorn, and I have a new illsight into the workings or my t)rain.
7 ' 1 1 ~ N(~urologkt.It was o u r Founding Editor, Robert Joynt, who first got me to wondering about which hemisphere I riormally speak with. H e would reawaken my interest yearly by remarking to the medical students, during his annual lecture o n aphasia (while I, their teacher, sat among them), "It will be interesting to see, when Dr. Goldblatt gets his stroke, whether o r not he becomes aphasic." With the spontaneity that rehearsal befbre a changing audience permits, I would retor-t, "It will be interesting to see if' you're still around when I get it." 7'lw N P U T O S C Z PRobert ~ / ~ Z YDoty ~ . is the premier neuroscientist at the Uriivcrsity of Rochester (and, by extension, in the world). H e recently entered a vigorous retirement that gave him enough time to have a chat with me about My ( h e and the duality
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David Goldhlutt, M.D.
of' brain organization. H e has thought about this kind of thing a long time-Sperry was a guest advisor on his doctoral committee. We talked about the monkey experiments in which he stimulated the striate cortex o n o n e side when the corpus callosurn was intact, training one hemisphere: when he then cut the corpus callosum, with the ingenious snare that he devisecl, and isolated the other hemisphere, it did not know the answer that the previously stimulated hemisphere could give.' If one hemisphere is trained with a visual stimulus through the visual pathway, when the optic chiasm has fir-st been split to confine the input to one hemisphere, the other side does learn the answer. ' I h e idea o f a unilateral engram would make sense, Doty said to me, as a means of doubling the mnemonic capacity of the brain, as he previously hypotl~esized,:~ "but if the system doesn't work that way, too bad: great theory but so what. We try to weasel out by suggesting that if the thought, the language learning, is originating in the cortex, that might make a difference. When things a r e coming in through the normal sensory channels, both hemispheres have access to t h e information. 'The big hooker in all of' the tachistoscopic experiments in intact man is that if you deliver a tachistoscopic stimulus to one hemisphere it may be in that hemisphere for 5 to 10 milliseconds. T h e n it gets over to the other hemisphere a n d so it's rattling around all over the place. What kind of laterality experiment is that?" I was intrigued by the idea that thoughts might be like the electrical stimuli, keeping their own company in a piece of cortex o r at least o n one side of'the brain a n d not the other. A second idea of use to me corlcerned the lirnitations of the corpus callosum, even when it is doing its best. To approach that, consider it at its worst. when it has been divided by a neurosurgecn. Iloty, in one of' his essay^,^ reviews an observation of' 'IFevarthen on a split-brain patient that "strikingly illustrates the power of'. . . brainstem switching of' visual consciousness." 'I'lle patie~ltwas to use her left hand to mark a white object o n a black cloth in the right visual field. However, she reported that the instant she began to move her left hand toward this object, it disappeared! In other words, as her attention shifted to her right hemisphere fi)r movement of the left hand, visual attention was also trauskrred from the right to the left visual half-field; without the corpus callosum and the anterior cornrnissure the visual world was ueatly partitioned between the right anti left hemispheres and which hemisphere "saw" dqmided on which was queried.' As for the corpus callosum at its best, and its limitations, that is a topic of present interest to Doty. H e has collaborated in a morphometrically 420
V0I.UME 11. NUMBER 4 I~I:'CEI\IBI:II I991
ljasecl postulate that requires intrahernispheric integration of' complex tasks of information processing, simply because repeated transcallosal passes must be too slow to do the job, given the conducting capacity of' the system, the spectrum of' conduction velocities availalde, and the distances involved. "If' the, presunlably overlapping, neural assemblies needed to handle overlapping tasks are clustered together, this would lead to hemispheric specialization. T h e prediction follows that the large brains of mammals such as elephants and cetaceans will also manifest a high degree of' hemispheric specialization."' Because of' the emotional character of the exclarnation I heard in my head, I was greatly interested, also, in Doty's thoughts on the subject of emotion. H e has reviewed the considerable clinical intormation concerning the dif'ftring effects on mood a n d behavior of lesions in the left versus the right hemisphere.“^" [I'lhe evidence is rather good that the two heniisp11erestno1-mally have different emotional outlooks, probably because of the unilaterality of the first-order co~mectionsfro111the aniygdala. How this difftrence in emotional tone of the two hemispheres is accomn~odated in normal individuals is as obscure as any other interchange between them. A well-documented case exists, however, in which the subject, initially troubled by ;~brupt,spontaneous emotional transitions, learned t o contl-ol these rnoods; laboratory findings n~uchlater revealed that her control was achieved by switching clominance f'rom one to the other hemisphere. [See Doty' f i r references omitted here.]
I n his characteristically meticulous way, Doty has assembled evidence for a startling idea: because there is "a central role for the amygdala in the expression, a n d probably the experience, of' emotion in man a n d animals . . . [and because] the amygdala shares with the hippocampus in primates a sparsity of interhemispheric connections, [should] 'sharing' [between the hemispheres] be impaired, the anatomical possibility also exists fbr each hemisphere to pursue a semi-independent emotional life!"" It is his belief that perturbation in the "dynamic equilibrium" of the two hemispheres, achieved normally through "neural competition," underlies schizophrenia. Abnorniality of featul-es reflecting interhemispheric processes is cornmou in schizophrenic patients; and the 'first-rank' symptoms o f delusions or hallucinations are prototypical of' what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is ti)cussed primal-ily through, the raphC serotonergic systern, that plays such a fundamental role iu consciousness, in dreaming, iu response to psyctlotonlirnetic drugs, and
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SEMINAKS IN NEUKOI,O(;Y
12ec;1usethis is not true, we cannot cxplailt the unity of a person's life by claiming that the expel-iericcs in this lifc are all had by this person. We can explain this unity only b y describing the various relations that hold between these diflkrcnt experiences, a n d their rclatiorls to a particular brain. We could therefore describe a pet.-
sott's life i n a n impersonal way, this person exists.
which does not claim tha
0 1 1 this Keductionis~View, persons d o exist. B U I they exist only in the u x y in which nations exist. Pet-son'are not, ;is we mistakenly believe, fu~idam~r~tcd. This vieu is in this sense more imperwn;~l.~~"'~
If' o u r identity is not what matters, what is i~ that does matter? "What matters," Parl'it concludes, i c -iohc~tmrtkrs us prrwns." What niatters i:. "psychological continuity antilor connectedness." H e ~vantsus to 11c clear that ' h o s t of us slioiildl change our view about the nature of' persons, and personal identity over time. T h e truth is here ver) ciif'f'erent from what niost of us belicve."'P'"' Hi:) truth about the "state of awareness" that exists within a disconnected hernispliere does offer a wa) to think about the paradox of the divided brain. but the reader who wishes to grasp it must turn to1 t to understancl him I'arfit's writings. I d o ~ i o claim well enough to epitomize his thought, and t h a t ' ~ not fair to a philosopher anyhow. My Ex/hwtion. 1 am, as I said, left-handed. My father and his sister (his only sibling) as well as both his parents were left-handed. I can f ~ i r l y claim that I came by my handedness naturally. although those who blame siriistrality on birth trauma have an argument in my case, since I experienced consideral~le fetal distress during my birth and was a "version a n d footling," as I have previously described. ' 1 have, however., been acculturated as a righthander for writing antl eating. Switching me to my right hand Ibr writing was acconiplished bv my parerits when 1 was a preschooler. Dad wrote righthanded, but that was because he had been fi)rced into it in school: he did not want to treat his first child the same way, but h e recognized the conve11ie11c:eof writing right-handed. So Mom and Dad ~tsetireward instead of' punishment to alter the behavior of their little boy: I had a blackboard. and when I attempted to draw o r to "write" o n it with chalk, left-handed, they would say, "'That's very nice, Ihvey; now show us what you can d o with your o t l ~ e rhand." When I then tried my right, ~ l i c ywould ~ i ~ u r m ua11 r approving "Ooh!" and praise my work. 'l'he flattery succeeded and, by the time I entered school, I was writing and drawing with my right hand, but I retained left-handedness for everything else arid was left-footed a n d left-eyed. I still play sports and d o home repairs left-handed antl I cut that way with scissors, despite the discomfbrt that the usual handles create. I was in my teens before I went along with the idea of holding a n eating utensil in my right hand, hilt it was a compromise, making me a two-fisted eater (knife in left
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111-obablyin tno\zcmcnt,m d even the tt-ophic state o f the tteocot-[ex.' 7 . h ~f ' f ~ i l ~ ~ oTphle~ stock ~ ~ . in trade of presentday philosophers seems to be problem cases, science-fictionlike situations in which brains are divided between diff'erent bodies, o r minds are fused, o r in which replicas of persons are sent to other planets, all in the interest of illuminatiiig questions of personal identity. I n an uninitiated person like me, these exarnples elicit two kinds of response: willingness to follow the analysis fin- the sake of the legitimacy of the question, o r ridicule because I have enough things to worry about without the silliness of half-brain transplants a n d of illstantaneous space travel-the odd kind that d s o leaves the traveler where he was to start with! Oxfbrcl philosopher Derek ParEit argues, not unpersuasively to a neurologist, that in even the extreme o r limiting case of' organ transplanlation-his brain into another body-"it may seem that I am here the dead donor. But I am really still the recipient, arid the ~ u r v i v o r . "I'art'it's ~ thinking is also accessible to the rieurologist when he turns to neuroanatomy a n d the split-brain expel-inients. Almost as quickly, however, h e turns the actual experinients into t h o u g h t - e x p e r i ~ s by , positing, for example, that h e can, by activating a switch attached to his eycbr-ow, disconnect the "exactly-siniilar-" hemispheres of' his brain. (He quite understantis that his brain is in that respect atypical; h e is making a n assurnptiori to develop his argument.) When we imagine the possibility that, in a briefly divided brain, two strearns of consciousness may How tfiroi~ghparallel channels and then, at the flick of a switch, reunite like the parallel streams o f a river flowing past an island, we must consider- the possibility that, during the time of separatioti, two persons have come into being within a single body. 'l'hat is 11y no means the only possib_ility.You will need to read him to get the idea of what he calls My Division: "Call one of the resulting people Lrlftj. I might ask, 'Are I& and Dorek Parfit names of' one and the same person?"' he writes, and goes on from Central to Parfit's thought is the idea that our k h t i t y i~snot wlm&mutt~rs.*-'~ H e powerfully contests the view of' 1)escartes and of' many others concerning an Ego, a person as a thinker of thoughts o r subject of experiences. As a supporter of the Keductionist view, h e disbelieves that we a w such "entities":
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42 1
resides in the right hernisphere of' those persons who speak primarily with the left hernispherc, arid that left-hantlers often have language capacity that is clistl-ibuted more evently between the herriispheres than right-1laritle1-s do."' It is no surprise that my r-ight brain easily had the capability of'calling me stupid. Dr. 1)oty's ot)scrvations, cited before, make me believe that, at a tirrie shortly after waking, when the alerting o r energizing influence of the brainstern is not fully operatio~ial,when I shifted my attention into my r-ight hemisphere hy catching sight of the scissors in niy left hand, I also "lighted up" the language capability of that hemisphere, which escaped the suppressive influence of the left and permitted the exclamation "Stupitl!" to be voiced internally. T h e analogy is with having enough power coming into the house through the basement to light only one of the two upstairs bedrooms at any one tirne. This is a different idea froni that of Parfit's eyebrow switch, which tlisconnects the hemispheres horizontally; but vulnerability of' the fi)rel)~-ainconiniissures to states of' impaired alertness, undue fatigue, intoxication, and the like cannot he excluded as a cause of physiologic cleconnection. If we accept that there are times when the alien voice of the r-ight hemisphere speaks in o u r heads, the reniaining question is, "How do we hear it?" 'I'he possible explanations are: ( 1 ) we hear it in the left brain, (2) we hear it in the right, and (:3) we hear it in t ~ o t h .It would not be fair t o add the brainstem as a site of recognition. We are, af'ter all, neurologists, not philosophers, and the premisses of our syllogisms have their limits. ' I h e "head ganglion" of the subcortical emotional system, the arnygdala, however, has a private relationship with its o w n hemisphere, as Doty points out, ant1 has the capability of' giving emotional tone and feeling to an utterance; to that extent, the subcortical system ( o n one side) may well be involved. My opinion allout My Case is that I heard the voice in my right brain-that, at that nlonicnt, tny consciousness was 1.ig1lt-heniisphcl-icin its locus. I cannot, after reading in Par-fit, clai~nthat I 7 m . s . briefly, a pcrsori whose right hemisphere was his brain, but at least that's where the action was. What I believe happens niuc:h niore often is that my right 1)rai11controls my left and makes it d o things it doesn't want to do. Onc last example is a piece of writing, called hly Experiment, with which 1 close this too-long essay. It has the antiintellectual quality I have been trying, all through this essay, to avoid a n d a flippancy o f t o n e that undermines what I have 1)eeli working so hard to get ;icross. I know very little about my right brain, of
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hand, spoon o r fork in right). A n d I can do syrnmetrical things two-handed, such as drawing a cross-section of the spinal cord o r the nledulla on the blackboard fbr my students, who seem to think they have "seen something amazing" (to use Auden's phrase), whereas for me it's easy. I believe that I speak with my left hemisphere. I can't use the way I hold a pencil as a way tojudge that, since I d o not hold it in my preferred l ~ a n d , if that is what I may call my left hand. I am a "pusher," not a "hooker," but I don't even know how I would have written lef't-handed without the model of my right to follow. Normal writing posture in both right-handers anti left-handers has been correlated with contralateral hemispheric specialization thr language and ipsilateral visuospatial superiority.".'" A n inverted writing posture indicates ip.silutrru1 language specialization arid contrcdnt~rnlspecialization for "n~eritalimagery and the understanding of spatial relationships": a reversed situation." Whether, i r i a left-hander who writes with the left hand, that hand is controlled by the right hemisphere after receiving its instructions transcallosally froni the left (if, as in the ma,jority of such cases, the left is the speech hernisphere) o r whether the left hand is contl-olled ipsilaterally for writing is not known.'" How can I infer that my left is my speech hernisphere? (This is what 1)r. Joynt first r i d e rile seriously consider.) I don't like to think about it, but I have to: my dad and his mother both had strokes, late in life, that affected the left side of the body. Dad's was embolic, in the territories of the right anterior anti rriiddle cerebral arteries. For a few days, his speech was slurred and he repeated what he had just said, probably to be sure I understood him (or maybe it was palilalia). For a longer time, his speech lacked prosody. Neither he nor his mother was aphasic. Knowing that about those left-handed per-sons with whom I am genetically linked is enough to convince me that I, too, speak with my left brain. Like many people, I talk to nlysrlf; arid I "hear" the words I read o r write. It slows me clown, but it is how my brain works. (Are you that way, also? If' so, you have my sympathy.) But there is all the difterence in the world between those usual, internally "voiced" thougl~ts(which are, I believe, of left hemispheric origin) anti the z~oiwthat once, and, thus far, once only, spoke to me and called me stupid. -1hat was, as I sensed at once, ttu~z w i r ~(4 my right hemisf)herr, speaking to itself loudly enough for- me to hear it. My recognition of "physiologic deconnectiori" was born. We know from the effect of left-brain strokes and hernispherectorny that interjectional speech
I n summary, let m e I-eiterate that what we have assun1c.d to be a real experiment by a real neuroscientist is only what has been relkrrecl to as a C;edankenexperiment, f'rom the ( k r r n a n word h r " l ' h a r ~ k you!" 'l'he good fortune of this is a p p a r e n t ,just when we realize that, if' the expel-inlent Ilad been a real o n e a n d il', f i ~ r thel-ac.c.epting the prerniss that all pl~ilosopherslook m d act alike-we wo~rlclhave n o way of krlowing which 01' them had undergone the surgery, we \vould b r left wit11 the ambiguous a n d unsatisfactory situation that, in any personal encounter with a philosopher, we might actually be speaking with philosopher A, who had t h e I x t i n of' a Brussels sprout, o r philosopher B, who had n o brairl at all.
,\.II. I:',x~errrtr~t1/. 11mgi11ethe lollowing cxpcriment: neul-oscicntist has in his laborato~-ytwo philosophers. A l t l ~ o r ~ geach h espouses ;I tlif'lkt.rnt school of' p l d o s o p h y (each is, illdeed. t h e only enrollee in each of those schools. where tuition is nierely recommentlcd a n d attentl;uicc is taken 1,ut not in ;I spirit o f hopefulness), h e y t~evet-thlcsslook identical to each other. (Iktails of this a r e u ~ l i r n p o r t ; ~ nmake t: some of their ftatut-es curly hair. a n d wil-e-ri~nmetlgl;~sses.I f you need this, ; ~ d da c.ol'1i.c (-1111 that has rlcvct- beet1 washed.) Now i ~ x ~ g i t lf e~ ~ r t h ethat r this neuroscientist has Besides my obvious debt to Bob Doty, I owe thanks just t.eturt~ed f'~.om;I I-wcck trip to a dista~lt galaxy where he has :I time-sh;tre ;mtl that, durirlg the I-eturn, to philosopher ,Jeltiey Spike, of the Division of Medical I I u t ~ ~ a n i t i cUniver-sity s, of' Kochester School of' Medicine Ire Ilas lef't hr.\ glasses, which m.c tinted t~ifocals,in the ;ird 1)entistl-y. 1 should also acknowledge the extetlt of sp;~ccship. 111) ignorance of'the subjects discussetl, but 1 believe that Notwithstanding, t h e neut-oscie~itistis hellbent o n 1 have alrcittly gotten that across in the text. his experiment, which irivolves retnoving the 11r;lins of' the philosophers. by means of'a recently perftcted technique in which Heineke11 beer is 11sec1as a perf'usate d u r ing t h e p~.vcedure,anti replacing them with ;I lest). vege t h l c . For this, the ~ ~ c u ~ - o s c i e nhxs t i s t a limited nunil)er REFERENCES of choices-the ~ r s l ~ a l liicceptrd ) urnhe her is live-sitice the intuitively obvious choices, caulitlo\vet. and cabbage, I . Ilalperti 1)F. (;oren S. H;tntlcclnc\s antl lilc span (Icttcr-). arc, pr;~ctically speaking, unavail;~lde becar~scof' their N Errgl ,I hletl 1W1 :324:01)8 large size. Since thcse five choices have I ~ e c ntlisc.ussetl at T lloty KLV. Klcctl-icalstimulatiorr of'thc brain in l x l ~ i~)ral a~ length previously (see my essay in Self a n d Shelf: O I I ~ contest. Atinu Krv 1's)cllol lCW);20:280-32O metaphysical 1a1-tier) let us settle o n one: the B r ~ ~ s s e l s 3. l h t y K\V, Ncgr-io N, Yarnag;~K . The u~rilatcralctrgt-am. spt-out. A t t ; ~Ncut-ohiol I
