320
Specialia
also in t h e frog t h e d e n s i t y of t h e n e u r o t u b u l e s a t t h e level of t h e spinal r o o t s p r o v e d t o b e lower in dorsal r o o t fibres t h a n in v e n t r a I root fibres. H o w e v e r , in t h e frog equal n u m b e r s of n e u r o t u b u l e s were f o u n d in m o t o r and s e n s o r y fibres i m m e d i a t e l y distal to t h e spinal ganglia. W e h a v e n o w f o u n d c o n s i d e r a b l y h i g h e r t u b u l a r densities in r a t s a p h e n o u s n e r v e fibres t h a n in M G N fibres of c o m p a r a b l e sizes. This fact suggests a n e v e n m o r e pron o u n c e d difference in t h e c o n t e n t of n e u r o t u b u l e s b e t w e e n m o t o r and s e n s o r y fibres of r a t p e r i p h e r a l nerves, w i t h lower v a l u e s for m o t o r n e r v e fibres t h a n t h o s e p r e s e n t e d for MGN in Table I; for it has to be t a k e n into a c c o u n t t h a t muscle n e r v e s like t h e MGN c o n t a i n a c o n s i d e r a b l e p e r c e n t a g e of sensory n e r v e fibres w h i c h could n o t be e x c l u d e d b y our s a m p l i n g t e c h n i q u e .
EXeEm~;NTIA 31/3
Zusamrne~c/assung. E s e r g a b sich, dass die Neurot u b u l u s d i c h t e in d e n A x o n e n eines H a u t n e r v e n ( R a t t e , N. saphenus) klar h b h e r ist als in gleich d i c k e n F a s e r n eines M u s k e l n e r v e n (N. g a s t r o c n e m i u s med.). E i n w e i t e r e r B e f u n d leistet einen B e i t r a g zt{r Erkl~Lrung dieses G e g e n s a t z e s : Die N e u r o t u b u l u s d i c h t e in d e n p e r i p h e r e n N e u r i t e n prim~irer sensibler N e u r o n e u n m i t t e l b a r distal des Spinalganglions (L~) ist s i g n i i i k a n t h 6 h e r als in d e n z e n t r a l e n N e u r i t e n in H 6 h e der H i n t e r w u r z e l W. ZENKER, R. MAYR a n d H. C-RUBER
2. A natomisches InsHtut der U~ziversitiit Wien, Wdhri~r 13, A-7090 Wien (Austria), # J u l y 7974.
Visual Cell Coding: Factoring Dioptric Responses from Maintained Discharge M a i n t a i n e d discharge, c o m m o n t h r o u g h o u t t h e visual s y s t e m , has tong f a s c i n a t e d a n d f r u s t r a t e d i n v e s t i g a t o r s ~-3. A l t h o u g h such a c t i v i t y is n o w generally a c c e p t e d as physiological, a n d i n d e e d vital, to t h e n o r m a l f u n c t i o n of t h a t sensory s y s t e m (see t h e c u r r e n t r e v i e w of LEvlCK ~), its v e r y p r e s e n c e c o m p l i c a t e s t h e d e c i p h e r i n g of t r a n s i e n t e v e n t signals m o v i n g in t h o s e p a t h w a y s W h i l e c o m p l e x models h a v e b e e n e x p l o r e d for t h e analysis of m a i n t a i n e d a c t i v i t y in t h e visual s y s t e m 5, c e r t a i n f o r m s of t r a n s i e n t i n f o r m a t i o n can a t t i m e s be e x t r a c t e d t h r o u g h v e r y f u n d a m e n t a l models, even in t h e p r e s e n c e of v e r y h i g h d e n s i t y 'noise' (e.g. 30 spikes/sec or more) g e n e r a t e d b y t h e c o n d u c t i n g neurone. The relative success of such r e d u c e d f a c t o r i n g models d e p e n d s , of course, on t h e r e g u l a r i t y of t h e m a i n t a i n e d discharge, a n d is i l l u s t r a t e d here in r e l a t i o n t o one of t h e m o s t f u n d a m e n t a l of t r a n s i e n t signals in t h e visual p a t h w a y s : t h e ongoing a s s e s s m e n t of i m a g e focus on t h e r e t i n a 6.
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1 H. K. HARTLINIsJ. cell. comp. Physiol. 5, 229 (1934). 2 E. D. ADRIAN',J. Physiol., Loud. 91, 66 (1937). 8 R. GRANIT, Acta physiol, seand. 7, 370 (1941). 4 W. R. LEVICK,Handbook o] Sensory Physiology (Springer-Verlag, New York 1973), vol. 7, part A, p. 575. H. B. BARLOWand W. R. LEVlC~, J. Physiol., Loud. 202, 699
I000
. . . . . . . .
o 03
ResponseD~spority for ActivityDrift
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The r e s p o n s e s cited are f r o m a m o n g s t a c u m u l a t i v e s a m p l e of m o r e t h a n 300 nero-ones w i t h i n t h e r a b b i t m e s e n c e p h a l o n a n d visual c o r t e x n o w s t u d i e d . T h e a n i m a l s were m a i n t a i n e d u n d e r light u r e t h a n e a n e s t h e s i a (6.0 m l / k g b o d y wt. of a 20% s o l u t i o n in saline, a dosage level f o u n d f r o m earlier w o r k to be no m o r e d e t r i m e n t a l t o cell r e s p o n s i v e n e s s t h a n ' e n c @ h a l e isol6' techniques). This was s u p p l e m e n t e d w i t h 3.3 m g / k g b o d y w t . / h of gallamine t r i e t h i o d i d e to p r e v e n t eye a n d b o d y m o v e m e n t s ,
.
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18 20
INDUCED RETINAL IMAGE BLUR (Dioptres)
Responses of a midbrain ceil to a black edge moviug across its receptive field once per sec, integrated over 30 sec periods. The test sets for each focal condition were spaced 90 sec apart, their order of presentation being indicated by the numbers next to the points. A) shows the actual spike totals recorded, i.e. without correction for maintained activity drift; t3) shows the same data, corrected for maintained activity drift (see text} ; and C) shows the maximum case of transient response distortion expected, calculated on the assumption that the data could have been collected in the particular order indicated.
15.3. 1975
Specialia
t h e a n i m a l b e i n g artificially r e s p i r a t e d d u r i n g t h a t period. The a n i m a l s were s u p p o r t e d s t e r e o t a x i c a l l y , t h e s t i m u l a t e d eye in e a c h case b e i n g r e f r a c t e d a n d f i t t e d w i t h a c o n t a c t lens to p r o t e c t t h e cornea f r o m d r y i n g a n d t o b r i n g t h e r e t i n a i n t o c o n j u g a c y w i t h t h e 57 c m d i s t a n t t e s t i n g plane. Stainless steel m i c r o - e l e c t r o d e s were i n t r o d u c e d into t h e visual c o r t e x a n d superior collieulus t h r o u g h a n agar sealed skull a p e r t u r e . Once localized in visual space, t h e r e c e p t i v e field of e a c h cell was m a p p e d t h r o u g h t h e n e u t r a l i z i n g r e f r a c t i v e c o r r e c t i o n for t h a t axis in space, using t h e m o s t c o m m o n l y o p t i m a l s t i m u l u s c o n d i t i o n s (a flashing 1 sec on, i sec off, 1/2~ d i a m e t e r , 4.1 c d / m 2 l i g h t s p o t a g a i n s t a 0.03 c d / m ~ b a c k g r o u n d ) . Occasionally, w h e n as d e s c r i b e d in t h e s e results, a cell r e s p o n d e d b e s t t o o t h e r stimuli, e.g., m o v e m e n t of a b l a c k edge a g a i n s t an 8 c d / m 2 b a c k g r o u n d , t h o s e m o r e o p t i m a l s t i m u l i were used t o m a p t h e field. The r e c e p t i v e field was t h e n r e p l o t t e d for each of a series of spherical (plus p o w e r t o induce m y o p i a ; m i n u s p o w e r to induce h y p e r o p i a ) r e f r a c t i v e errors b y c e n t e r i n g t h e i n d u c i n g lenses on t h e r e c e p t i v e field axis. R e c o r d i n g sites were l a t e r c o n f i r m e d b y P r u s s i a n blue m a r k s localized in frozen sections m a d e of each brain. The F i g u r e shows, for a p h o t i c a l l y r e s p o n s i v e m i d b r a i n cell (in t h e s t r a t u m o p t i c u m of t h e superior colliculus), spike t o t a l s i n t e g r a t e d over 30 sec p e r i o d s d u r i n g w h i c h t i m e a b l a c k edge was p a s s e d t h r o u g h its r e c e p t i v e field f r o m a l t e r n a t e d i r e c t i o n s once each second a t t h e cell's o p t i m u m r e s p o n s e v e l o c i t y of 12~ Figure A shows t h e a c t u a l spike t o t a l s r e s u l t i n g f r o m t h i s s t i m u l u s p r o c e d u r e as t h e y were r e c o r d e d over a wide r a n g e of eye focus conditions. F i g u r e B shows t h i s s a m e d a t a , a f t e r t h e m a i n t a i n e d d i s c h a r g e of t h e cell was linearly c o r r e c t e d for d r i f t (i.e. b a s e d on t h e spike t o t a l s over 30 sec i n t e r v a l s w i t h o u t t h e m o v i n g edge present), using t h e following m o d e l 7:
Figure C r e p r e s e n t s t h e m a x i m u m case (calcuIated b y t h e m o d e l above) of t r a n s i e n t r e s p o n s e d i s t o r t i o n due to t h e m a i n t a i n e d a c t i v i t y d r i f t of t h i s cell, w h i c h could h a v e r e s u l t e d f r o m t a k i n g t h e d a t a in t h e p a r t i c u l a r s e q u e n c e i n d i c a t e d in t h e Figure. The f u n d a m e n t a l a s s u m p t i o n w h e r e such a c o r r e c t i o n m o d e l is a p p l i e d is, of course, t h a t l i n e a r i t y of t h e m a i n t a i n e d a c t i v i t y d r i f t is e s s e n t i a l l y c o n s t a n t over t h e t e s t i n g p e r i o d e n c o m p a s s e d s. I n t h e case of t h e p a r t i c u l a r cell i l l u s t r a t e d in t h e Figure, one t e s t a p p l i e d was to r e p e a t t h e first focal c o n d i t i o n (i.e. p e r f e c t s h a r p n e s s of t h e r e t i n a l image) once again a t t h e end of t h e e n t i r e focal series. As can be seen in F i g u r e B, t h e c o n s i s t e n c y of t h e c o r r e c t e d r e s p o n s e (using t h e linear model) was
321
w i t h i n 2% of t h e original r e s p o n s e to t h a t c o n d i t i o n m e a s u r e d 12 mill previously. This was so, e v e n t h o u g h t h e m a i n t a i n e d b a c k g r o u n d a c t i v i t y h a d increased b y m o r e t h a n 50% over t h a t s a m e p e r i o d of t i m e , f r o m 22 up t o 34 spikes/sec. Two conclusions m i g h t t h e n be s u p p o r t e d f r o m t h e s e o b s e r v a t i o n s : first, t h a t t h e gain f u n c t i o n s of t h e t r a n s i e n t signal a c t i v i t y a n d of t h e b a c k g r o u n d a c t i v i t y n e e d n o t be rigidly t i e d 9, a n d second, t h a t t h e 'analyzer(s)' of t o t a l spike a c t i v i t y , m a k i n g up such a c h a n n e l as described here, m a y well be d o i n g a similar k i n d of correction (linear, sinusoidal or of some o t h e r m o r e c o m p l e x form) in o r d e r t o p r e s e r v e t h e q u a n t i t a t i v e i n t e g r i t y of t h e t r a n s i e n t signal code. S u c h a c o r r e c t i o n h o w e v e r w o u l d s e e m to require, as here, a close c o m p a r a t i v e cognizance of b o t h signal a n d m a i n t a i n e d a c t i v i t y a t a n y p a r t i c u l a r t i m e .
Zusammen/assung. Die Iokalen R e a k t i o n e n der p h o t i s c h e n Zellen auf d u r c h g e h e n d e A n r e g u n g e n erwiesen sich als q u a n t i t a t i v gleichm~ssig, dies sogar bei w e c h s e l n d g e h a l t e n e r AktivitS.t. G. D. RITCHIE, J. E. SHEEDY, W. W. SOMERS a n d R. M. HILL1~
Comparative and Physiological Psychology, and College o/ Optometry, The Ohio State University, 338 West Tenth Avenue, Columbus (Ohio 43270, USA), 14 October 7974.
7 R is defined as the specific response to the transient stimulus presented (i.e. the moving black edge during a particular focal condition), N is the total number of spikes counted during the sampling interval (i.e. 30 see here) So is the rate of the maintained discharge just previous to starting the stimulus sequence described, Q is the number of intervals within which stimulus-response counts (one for each focal condition) were made, these intervals all being of equal length, t, and evenly distributed in time, and d S being the net increase of the maintained discharge rate over the entire experimental period, i.e., from just before the t1 interval for the first focal condition to just following the te interval for the last focal condition tested. s Rather than a linear drift, some cells do show sufficiently cyclic patterns of their maintained discharge that such activity can be described, and thus neutralized, using a basic sinusoidal model of the form :
in which A is the sinusoidal amplitude (in spike frequency) and T is the sinusoidal period, t here is elapsed time and all other terms are defined as previously. 9 H. SUZUKIand E. IZATO,J. Neurophysiol. 29, 909 (1966). 10 This work was supported by a grant from the USPHS National Eye Institute. We thank T. G. GAST and A. A. LEE for their assistance.
Pineal Body: Neuronal Recording I n r e c e n t y e a r s i n t e r e s t in t h e p i n e a l b o d y (PB) has increased c o n s i d e r a b l y . The P B has n o w b e e n s h o w n t o be a n e n d o c r i n e c o n t r o l l i n g o r g a n 1. I t is likely t h a t it c o n t r o l s t h e p e r i p h e r a l organs of i n t e r n a l secretion b y a m e c h a n i s m w h i c h i n v o l v e s t h e c o n v e r s i o n of 5 H T (serotonin) to m e l a t o n i n 2. Histological a n d e l e c t r o n m i c r o s c o p i c (EM) s t u d i e s on t h e c y t o a r c h i t e c t u r e of t h e P B are controversial. KAPPERS 3 r e p o r t e d t h a t in t h e rat, t h e m a j o r i t y of n e r v e fibres
e n t e r b i l a t e r a l l y f r o m t h e s u p e r i o r cervical ganglia via t h e n e r v i conarii, while only a b b e r a n t fibres were o b s e r v e d c o u r s i n g u p t h e e p i p h y s e a t stalk. H o w e v e r , in o t h e r m a m m a l s d e f i n i t e h a b e n u l a r i n n e r v a t i o n has b e e n J. AXELROD, Science 184, 1341 (1974). 2 H. WEISSBACn, B. G. REDFIELD and J. AXELROD, Biochim. biophys. Aeta d3, 352 (1960). 8 j. A. KAFFERS,Z. Zellforsch. 52, 163 (1960).
Specialia
also in t h e frog t h e d e n s i t y of t h e n e u r o t u b u l e s a t t h e level of t h e spinal r o o t s p r o v e d t o b e lower in dorsal r o o t fibres t h a n in v e n t r a I root fibres. H o w e v e r , in t h e frog equal n u m b e r s of n e u r o t u b u l e s were f o u n d in m o t o r and s e n s o r y fibres i m m e d i a t e l y distal to t h e spinal ganglia. W e h a v e n o w f o u n d c o n s i d e r a b l y h i g h e r t u b u l a r densities in r a t s a p h e n o u s n e r v e fibres t h a n in M G N fibres of c o m p a r a b l e sizes. This fact suggests a n e v e n m o r e pron o u n c e d difference in t h e c o n t e n t of n e u r o t u b u l e s b e t w e e n m o t o r and s e n s o r y fibres of r a t p e r i p h e r a l nerves, w i t h lower v a l u e s for m o t o r n e r v e fibres t h a n t h o s e p r e s e n t e d for MGN in Table I; for it has to be t a k e n into a c c o u n t t h a t muscle n e r v e s like t h e MGN c o n t a i n a c o n s i d e r a b l e p e r c e n t a g e of sensory n e r v e fibres w h i c h could n o t be e x c l u d e d b y our s a m p l i n g t e c h n i q u e .
EXeEm~;NTIA 31/3
Zusamrne~c/assung. E s e r g a b sich, dass die Neurot u b u l u s d i c h t e in d e n A x o n e n eines H a u t n e r v e n ( R a t t e , N. saphenus) klar h b h e r ist als in gleich d i c k e n F a s e r n eines M u s k e l n e r v e n (N. g a s t r o c n e m i u s med.). E i n w e i t e r e r B e f u n d leistet einen B e i t r a g zt{r Erkl~Lrung dieses G e g e n s a t z e s : Die N e u r o t u b u l u s d i c h t e in d e n p e r i p h e r e n N e u r i t e n prim~irer sensibler N e u r o n e u n m i t t e l b a r distal des Spinalganglions (L~) ist s i g n i i i k a n t h 6 h e r als in d e n z e n t r a l e n N e u r i t e n in H 6 h e der H i n t e r w u r z e l W. ZENKER, R. MAYR a n d H. C-RUBER
2. A natomisches InsHtut der U~ziversitiit Wien, Wdhri~r 13, A-7090 Wien (Austria), # J u l y 7974.
Visual Cell Coding: Factoring Dioptric Responses from Maintained Discharge M a i n t a i n e d discharge, c o m m o n t h r o u g h o u t t h e visual s y s t e m , has tong f a s c i n a t e d a n d f r u s t r a t e d i n v e s t i g a t o r s ~-3. A l t h o u g h such a c t i v i t y is n o w generally a c c e p t e d as physiological, a n d i n d e e d vital, to t h e n o r m a l f u n c t i o n of t h a t sensory s y s t e m (see t h e c u r r e n t r e v i e w of LEvlCK ~), its v e r y p r e s e n c e c o m p l i c a t e s t h e d e c i p h e r i n g of t r a n s i e n t e v e n t signals m o v i n g in t h o s e p a t h w a y s W h i l e c o m p l e x models h a v e b e e n e x p l o r e d for t h e analysis of m a i n t a i n e d a c t i v i t y in t h e visual s y s t e m 5, c e r t a i n f o r m s of t r a n s i e n t i n f o r m a t i o n can a t t i m e s be e x t r a c t e d t h r o u g h v e r y f u n d a m e n t a l models, even in t h e p r e s e n c e of v e r y h i g h d e n s i t y 'noise' (e.g. 30 spikes/sec or more) g e n e r a t e d b y t h e c o n d u c t i n g neurone. The relative success of such r e d u c e d f a c t o r i n g models d e p e n d s , of course, on t h e r e g u l a r i t y of t h e m a i n t a i n e d discharge, a n d is i l l u s t r a t e d here in r e l a t i o n t o one of t h e m o s t f u n d a m e n t a l of t r a n s i e n t signals in t h e visual p a t h w a y s : t h e ongoing a s s e s s m e n t of i m a g e focus on t h e r e t i n a 6.
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1 H. K. HARTLINIsJ. cell. comp. Physiol. 5, 229 (1934). 2 E. D. ADRIAN',J. Physiol., Loud. 91, 66 (1937). 8 R. GRANIT, Acta physiol, seand. 7, 370 (1941). 4 W. R. LEVICK,Handbook o] Sensory Physiology (Springer-Verlag, New York 1973), vol. 7, part A, p. 575. H. B. BARLOWand W. R. LEVlC~, J. Physiol., Loud. 202, 699
I000
. . . . . . . .
o 03
ResponseD~spority for ActivityDrift
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The r e s p o n s e s cited are f r o m a m o n g s t a c u m u l a t i v e s a m p l e of m o r e t h a n 300 nero-ones w i t h i n t h e r a b b i t m e s e n c e p h a l o n a n d visual c o r t e x n o w s t u d i e d . T h e a n i m a l s were m a i n t a i n e d u n d e r light u r e t h a n e a n e s t h e s i a (6.0 m l / k g b o d y wt. of a 20% s o l u t i o n in saline, a dosage level f o u n d f r o m earlier w o r k to be no m o r e d e t r i m e n t a l t o cell r e s p o n s i v e n e s s t h a n ' e n c @ h a l e isol6' techniques). This was s u p p l e m e n t e d w i t h 3.3 m g / k g b o d y w t . / h of gallamine t r i e t h i o d i d e to p r e v e n t eye a n d b o d y m o v e m e n t s ,
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18 20
INDUCED RETINAL IMAGE BLUR (Dioptres)
Responses of a midbrain ceil to a black edge moviug across its receptive field once per sec, integrated over 30 sec periods. The test sets for each focal condition were spaced 90 sec apart, their order of presentation being indicated by the numbers next to the points. A) shows the actual spike totals recorded, i.e. without correction for maintained activity drift; t3) shows the same data, corrected for maintained activity drift (see text} ; and C) shows the maximum case of transient response distortion expected, calculated on the assumption that the data could have been collected in the particular order indicated.
15.3. 1975
Specialia
t h e a n i m a l b e i n g artificially r e s p i r a t e d d u r i n g t h a t period. The a n i m a l s were s u p p o r t e d s t e r e o t a x i c a l l y , t h e s t i m u l a t e d eye in e a c h case b e i n g r e f r a c t e d a n d f i t t e d w i t h a c o n t a c t lens to p r o t e c t t h e cornea f r o m d r y i n g a n d t o b r i n g t h e r e t i n a i n t o c o n j u g a c y w i t h t h e 57 c m d i s t a n t t e s t i n g plane. Stainless steel m i c r o - e l e c t r o d e s were i n t r o d u c e d into t h e visual c o r t e x a n d superior collieulus t h r o u g h a n agar sealed skull a p e r t u r e . Once localized in visual space, t h e r e c e p t i v e field of e a c h cell was m a p p e d t h r o u g h t h e n e u t r a l i z i n g r e f r a c t i v e c o r r e c t i o n for t h a t axis in space, using t h e m o s t c o m m o n l y o p t i m a l s t i m u l u s c o n d i t i o n s (a flashing 1 sec on, i sec off, 1/2~ d i a m e t e r , 4.1 c d / m 2 l i g h t s p o t a g a i n s t a 0.03 c d / m ~ b a c k g r o u n d ) . Occasionally, w h e n as d e s c r i b e d in t h e s e results, a cell r e s p o n d e d b e s t t o o t h e r stimuli, e.g., m o v e m e n t of a b l a c k edge a g a i n s t an 8 c d / m 2 b a c k g r o u n d , t h o s e m o r e o p t i m a l s t i m u l i were used t o m a p t h e field. The r e c e p t i v e field was t h e n r e p l o t t e d for each of a series of spherical (plus p o w e r t o induce m y o p i a ; m i n u s p o w e r to induce h y p e r o p i a ) r e f r a c t i v e errors b y c e n t e r i n g t h e i n d u c i n g lenses on t h e r e c e p t i v e field axis. R e c o r d i n g sites were l a t e r c o n f i r m e d b y P r u s s i a n blue m a r k s localized in frozen sections m a d e of each brain. The F i g u r e shows, for a p h o t i c a l l y r e s p o n s i v e m i d b r a i n cell (in t h e s t r a t u m o p t i c u m of t h e superior colliculus), spike t o t a l s i n t e g r a t e d over 30 sec p e r i o d s d u r i n g w h i c h t i m e a b l a c k edge was p a s s e d t h r o u g h its r e c e p t i v e field f r o m a l t e r n a t e d i r e c t i o n s once each second a t t h e cell's o p t i m u m r e s p o n s e v e l o c i t y of 12~ Figure A shows t h e a c t u a l spike t o t a l s r e s u l t i n g f r o m t h i s s t i m u l u s p r o c e d u r e as t h e y were r e c o r d e d over a wide r a n g e of eye focus conditions. F i g u r e B shows t h i s s a m e d a t a , a f t e r t h e m a i n t a i n e d d i s c h a r g e of t h e cell was linearly c o r r e c t e d for d r i f t (i.e. b a s e d on t h e spike t o t a l s over 30 sec i n t e r v a l s w i t h o u t t h e m o v i n g edge present), using t h e following m o d e l 7:
Figure C r e p r e s e n t s t h e m a x i m u m case (calcuIated b y t h e m o d e l above) of t r a n s i e n t r e s p o n s e d i s t o r t i o n due to t h e m a i n t a i n e d a c t i v i t y d r i f t of t h i s cell, w h i c h could h a v e r e s u l t e d f r o m t a k i n g t h e d a t a in t h e p a r t i c u l a r s e q u e n c e i n d i c a t e d in t h e Figure. The f u n d a m e n t a l a s s u m p t i o n w h e r e such a c o r r e c t i o n m o d e l is a p p l i e d is, of course, t h a t l i n e a r i t y of t h e m a i n t a i n e d a c t i v i t y d r i f t is e s s e n t i a l l y c o n s t a n t over t h e t e s t i n g p e r i o d e n c o m p a s s e d s. I n t h e case of t h e p a r t i c u l a r cell i l l u s t r a t e d in t h e Figure, one t e s t a p p l i e d was to r e p e a t t h e first focal c o n d i t i o n (i.e. p e r f e c t s h a r p n e s s of t h e r e t i n a l image) once again a t t h e end of t h e e n t i r e focal series. As can be seen in F i g u r e B, t h e c o n s i s t e n c y of t h e c o r r e c t e d r e s p o n s e (using t h e linear model) was
321
w i t h i n 2% of t h e original r e s p o n s e to t h a t c o n d i t i o n m e a s u r e d 12 mill previously. This was so, e v e n t h o u g h t h e m a i n t a i n e d b a c k g r o u n d a c t i v i t y h a d increased b y m o r e t h a n 50% over t h a t s a m e p e r i o d of t i m e , f r o m 22 up t o 34 spikes/sec. Two conclusions m i g h t t h e n be s u p p o r t e d f r o m t h e s e o b s e r v a t i o n s : first, t h a t t h e gain f u n c t i o n s of t h e t r a n s i e n t signal a c t i v i t y a n d of t h e b a c k g r o u n d a c t i v i t y n e e d n o t be rigidly t i e d 9, a n d second, t h a t t h e 'analyzer(s)' of t o t a l spike a c t i v i t y , m a k i n g up such a c h a n n e l as described here, m a y well be d o i n g a similar k i n d of correction (linear, sinusoidal or of some o t h e r m o r e c o m p l e x form) in o r d e r t o p r e s e r v e t h e q u a n t i t a t i v e i n t e g r i t y of t h e t r a n s i e n t signal code. S u c h a c o r r e c t i o n h o w e v e r w o u l d s e e m to require, as here, a close c o m p a r a t i v e cognizance of b o t h signal a n d m a i n t a i n e d a c t i v i t y a t a n y p a r t i c u l a r t i m e .
Zusammen/assung. Die Iokalen R e a k t i o n e n der p h o t i s c h e n Zellen auf d u r c h g e h e n d e A n r e g u n g e n erwiesen sich als q u a n t i t a t i v gleichm~ssig, dies sogar bei w e c h s e l n d g e h a l t e n e r AktivitS.t. G. D. RITCHIE, J. E. SHEEDY, W. W. SOMERS a n d R. M. HILL1~
Comparative and Physiological Psychology, and College o/ Optometry, The Ohio State University, 338 West Tenth Avenue, Columbus (Ohio 43270, USA), 14 October 7974.
7 R is defined as the specific response to the transient stimulus presented (i.e. the moving black edge during a particular focal condition), N is the total number of spikes counted during the sampling interval (i.e. 30 see here) So is the rate of the maintained discharge just previous to starting the stimulus sequence described, Q is the number of intervals within which stimulus-response counts (one for each focal condition) were made, these intervals all being of equal length, t, and evenly distributed in time, and d S being the net increase of the maintained discharge rate over the entire experimental period, i.e., from just before the t1 interval for the first focal condition to just following the te interval for the last focal condition tested. s Rather than a linear drift, some cells do show sufficiently cyclic patterns of their maintained discharge that such activity can be described, and thus neutralized, using a basic sinusoidal model of the form :
in which A is the sinusoidal amplitude (in spike frequency) and T is the sinusoidal period, t here is elapsed time and all other terms are defined as previously. 9 H. SUZUKIand E. IZATO,J. Neurophysiol. 29, 909 (1966). 10 This work was supported by a grant from the USPHS National Eye Institute. We thank T. G. GAST and A. A. LEE for their assistance.
Pineal Body: Neuronal Recording I n r e c e n t y e a r s i n t e r e s t in t h e p i n e a l b o d y (PB) has increased c o n s i d e r a b l y . The P B has n o w b e e n s h o w n t o be a n e n d o c r i n e c o n t r o l l i n g o r g a n 1. I t is likely t h a t it c o n t r o l s t h e p e r i p h e r a l organs of i n t e r n a l secretion b y a m e c h a n i s m w h i c h i n v o l v e s t h e c o n v e r s i o n of 5 H T (serotonin) to m e l a t o n i n 2. Histological a n d e l e c t r o n m i c r o s c o p i c (EM) s t u d i e s on t h e c y t o a r c h i t e c t u r e of t h e P B are controversial. KAPPERS 3 r e p o r t e d t h a t in t h e rat, t h e m a j o r i t y of n e r v e fibres
e n t e r b i l a t e r a l l y f r o m t h e s u p e r i o r cervical ganglia via t h e n e r v i conarii, while only a b b e r a n t fibres were o b s e r v e d c o u r s i n g u p t h e e p i p h y s e a t stalk. H o w e v e r , in o t h e r m a m m a l s d e f i n i t e h a b e n u l a r i n n e r v a t i o n has b e e n J. AXELROD, Science 184, 1341 (1974). 2 H. WEISSBACn, B. G. REDFIELD and J. AXELROD, Biochim. biophys. Aeta d3, 352 (1960). 8 j. A. KAFFERS,Z. Zellforsch. 52, 163 (1960).
