Physiology& Behavior, Vol. 50, pp. 881-885. ©PergamonPress plc, 1991.Printedin the U.S.A,
0031-9384/91 $3.00 + .00
Chlorpromazine and the Lateralisation of the Perception of Emotion L. R. HARTLEY, L. K. IRELAND, P. K. ARNOLD AND J. SPENCER
Department of Psychology, Murdoch University, Western Australia 6150 Received 22 January 1991 HARTLEY, L. R., L. K. IRELAND, P. K. ARNOLD AND J. SPENCER. Chlorpromazineand the lateralisation of the perception of emotion. PHYSIOL BEHAV 50(5) 881-885, 1991.--In a double-blinddesign, sixteen volunteer students were administered 50 nag of chlorpromazineor a placebo in tablet form on separate occasions, two hours prior to testing. The test was a lexical decision paradigm involvingunilateralpresentationof pairs of neutral, positive and negativeemotionalwords and nonwordsto the left or right visual fields. Reactiontime to identify words and nonwords was recorded. Neutral stimuli were processed faster in the left hemisphere, while negative stimuli were processed faster in the right hemisphere. Chiorpromazineimproved speed of response for neutral stimuli presented to the right hemisphere and for affective stimuli presented to the left hemisphere. Thus chiorpromazine seems to benefit right hemisphere processing of nonaffective stimuli and benefit left hemisphere processing of affective stimuli. Chiorpromazineappeared to have a different impact on neutral and affective words, and on the right and the left hemispheres. The general effect of chiorpromazine was to reduce lateralisation.It was suggested that this occurred because chlorpromazine blocked dopamineand possibly other neurotransmitters. Chiorpromazine Word pair
Lateralisation
Emotion
Human
RECENT findings suggest that the processing of not only language (1, 5, 19) but emotional stimuli may be lateralised to the cerebral hemispheres. Several lines of evidence implicate the right hemisphere in processing emotional stimuli. Results of studies of dichotic listening (2, 4, 16), tachistoseopic presentation (15,21), facial expression (18) and hysterical neurosis (8) have all indicated a right hemisphere dominance in the processing of emotional material. In addition, Tucker (23) proposed, on the basis of studies of psychopathologics and unilateral brain damage, as well as normal subjects, that the processing of emotional valence may be lateralised. Such studies suggest that the left hemisphere may be specialized for processing positive affect, as damage in this hemisphere leads to greater expression of negative emotion. In contrast, damage or suppression of the fight hemisphere typically results in a euphoric-manic reaction (20), suggesting the right hemisphere is responsible for processing negative affect. Buck has further suggested (3) that affective information passes from the limbic system to the frontal lobes of both hemispheres, though more directly to the fight hemisphere. Output from the left hemisphere concerns higher order affective processes, such as anxiety, while the fight hemisphere reports on primary emotions (3). Tucker and Williamson (24) have noted the asymmetrical distribution of some neurotransmitters in animal and human brain (11,12). While norepinephrine and 5-HT pathways are lateralised to the fight hemisphere, dopamine pathways are abundant in the left hemisphere, and stimulation of the dopamine
Dopamine
Affectcondition
Visualfield
pathways results in an asymmetric increase in motor function (9). The dopamine system has been shown to have an excitatory influence on motor behaviour (7,14), and may have a role in active attentional processes by coordinating motor output with perceptual information (24). The evidence briefly reviewed above suggests there may be a relationship between affect, hemispheric arousal and dopamine. This study, therefore, examined the lateralisation of the perception of affective words and whether the extent of the lateralisation was influenced by chlorpromazine. Pairs of verbal stimuli were laterally presented to each visual field, and the speed of their perception recorded. Stimuli presented to the left visual field are assumed tO be fast processed by the fight cerebral hemisphere and vice ~ersa for stimuli presented to the fight visual field. The fast stimulus in the pair was a word and the second was either a related word or a nonword. The study required subjects to decide whether the second stimulus was a word or nonword. It was expected that word-word pairs would be responded to faster than word-nonword pairs as words are processed faster than nonwords (6,17). It was also expected that the perception of neutral stimuli would be faster in the fight visual field as the left hemisphere is the prime linguistic processor. If emotion is primarily processed in the right hemisphere (1,16), then it would be anticipated that emotional stimuli would be perceived faster in the left visual field. If chlorpromazine blocks the lateralised dopamine system then the drug should reduce any lateralisation of the perception of emotional words.
881
882
HARTLEY, IRELAND, ARNOLD AND SPENCER
TABLE 1 Word Prime--Word Target
T A B L E 1 (continued)
Word Prime--Nonword Target
Neutral Stimuli Arm--Leg C a m p - - Tent Cat -- Dog Hide--Seek Hour--Time Lark -- Bird Amount-- Money Mother -- Father Q u e e n - King Reflex -- Action Dream -- Sleep Sky--Blue Soil--Dirt Sugar-- Sweet Wigwam -- Indian City --Town Frog--Toad Boat-- Sail Author -- Writer Shoe-- Sock Hint--Clue Aunty--Uncle River--Water Read-- Book Moon-- Star Car-- Bus Bath-- Soap Season--Summer Figure -- Number Head -- Hair Tree--Leaf Paper -- Pencil Plant--Green Hot--Fan Cup--Mug Pot--Pan Letter -- Parcel Bike--Ride A r m y - - Navy Black--White
Arrn--Lig Camp -- Tont Cat-- Rog Hide--Ceek Hour--Tome Lark-- Berd Amount -- Siney Mother -- Futher Q u e e n - Kang Reflex -- Axtios Dream-- Sleop Sky--Brue Soil--Dirl Sugar-- Sweel Wigwam-- Insief City--Toan Frog--Toas Boat-- Saim Author -- Wriser Shoe--Seck Hint--Clum Aunty--Onkle River--Worte Read -- B oak Moon-- Ster Car -- Bas Bath--Stap Season-- Sommer Figure -- Namber Head-- Sair Tree--Leof Paper -- Dencil Plant--Greep Hot--Fon Cup--Mig Pot--Pag Letter -- Parncel Bike--Rime A r m y - - Novy Black--Chite Positive Stimuli
Love--Kiss Joy -- Glee Peace-- Loyal Bride --Bliss Merry-- Happy Laugh -- Smile Adore -- Amuse Lover -- Marry Thrill-- Praise Friend -- Warmth Excite-- Humour Cuddle -- Caress Tender -- Honour Success -- Delight Emotion-- Feeling Romance -- Passion Sensual -- Intense
Love--Kest Joy -- Glea Peace-- Lodal Bride--Brids Merry-Lapsy Laugh-- Spole Adore-- Amose Lover -- Monny Thrill-- Proote Friend-- Wemth Excite -- Hotour Cuddle -- Core st Tender -- Hodoar Success-- Doleght Emotion -- Doesint Romance-- Pestion Sensual-- Ontinze
Word Prime--Word Target
Word Prime--Nonword l'arget
Pleasure--Tranquil Fun--Hug Joyous--Special
Pleasure- Tridsoal Fun--Ric Joyous--Sleciol Negative Stimuli
Cry -- War Death--Ghost Grief--Mourn Drown-- Loathe Devil -- Satan Agony--Cruel Enemy --Panic Corpse -- Scream Suffer -- Misery Murder -- Behead Sorrow -- Funeral C a n c e r - Savage Horror -- Terror Molest-- Malice Kill-- Slay Stab-- Pain Hell -- Hate Despair--Jealous Repulse--Disgust Execute--Torture
Cry -- Wot Death--Grost Grief--Poard Drown -- Goetre Devil -- Jouse Agony-- Snuke Enemy-- Speol Corpse-- Presem Suffer -- Masard Murder -- Somead Sorrow-- Fanotal C a n c e r - Setuge Horror -- Patmar Molest -- Charch Kill -- Ladi Stab -- Deok Hell -- Coud Despair-- Deokous Repulse--Tistere Execute--Gondare
METHOD
Subjects Eight m a l e and eight female university students aged 2 0 - 2 9 years participated in the study. E a c h subject gave i n f o r m e d consent and n o n e h a d a n y health p r o b l e m s , including brain or liver d a m a g e , p r e g n a n c y or illness. Subjects were selected on the basis o f their score o n the E d i n b u r g h H a n d e d n e s s Inventory (5) indicating right h a n d e d n e s s .
Stimuli Stimuli were letter strings c o m p r i s i n g pairs o f w o r d s or nonw o r d s o f 3 - 8 letters a n d 1 - 3 syllables as s h o w n in T a b l e 1. S t i m u l u s pairs were presented on a V D U screen in block capitals lateralised to each visual hemifield. T h e s t i m u l u s pairs consisted o f a p r i m e w o r d followed b y either a related target word (e.g., A R M - - L E G ) or target n o n w o r d (e.g., A R M - - L I G ) o f similar length a n d n u m b e r o f syllables. Prime a n d target w o r d s were d r a w n f r o m the s a m e affective category a n d were E n g l i s h n o u n s in c o m m o n u s a g e and classified according to their e m o t i o n a l c o n t e n t as neutral, positive or negative. E i g h t y neutral w o r d s were selected f r o m the M o n a s h Free A s s o c i a t i o n N o r m s (22) to c o m p r i s e 40 neutral pairs o f stimuli. T e n i n d e p e n d e n t j u d g e s rated 100 positive and 100 negative n o u n s for emotionality. T h e 40 w o r d s rated as m o s t positive and 40 w o r d s rated as m o s t negative were selected to c o m p r i s e 20 pairs o f positive and 20 pairs o f negative stimuli. N o n w o r d s were nonaffective and were c o n s t r u c t e d b y c h a n g i n g one or m o r e letters in a target word to r e n d e r t h e m m e a n i n g l e s s but orthographically legal.
CHLORPROMAZINE, LATERALISATION AND EMOTION
883
TABLE 2 MEANREACTIONTIMES(IN ms) Chlorpromazine
Placebo LVF
Neutral Positive Negative
LVF
RVF
RVF
W
NW
W
NW
W
NW
W
NW
525 518 533
656 670 613
480 573 568
647 639 621
491 519 502
603 615 582
481 505 495
577 606 582
Design
The experiment was a 2 (drug) x 2 (word pair type) × 3 (affect) × 2 (visual field) design with repeated measures on all variables. Two dependent variables, reaction time to correct decisions and number of errors, were recorded. Subjects were administered a placebo and a 50-mg chlorpromazine tablet on two separate occasions two hours before testing under double-blind conditions. Half the subjects received the placebo first, while the other half received chlorpromazine first. Procedure
Each subject was required to attend a practice session a minimum of two days before the first testing session. Testing sessions were scheduled a week apart at the same time of day. Subjects received their tablet two hours before testing. Prior to each testing session, subjects were given 50 practice trials to refamiliarise them with the task. During testing, subjects received 200 trials with 40 pairs of neutral stimuli, 200 trials with 20 pairs of positive stimuli and 200 trials with the 20 pairs of negative stimuli. Stimuli were presented in blocks of 100 trials of each affective class. Equal numbers of word-word and word-nonword pairs were presented in each affect condition. Presentation order of blocks of 100 stimuli of each affective class was balanced by a Latin Square design. Presentation of the different stimulus conditions was also balanced across the visual fields. Throughout the experiment, a fixation dot remained in the centre of the VDU screen. Stimulus pairs were randomly presented, at a visual angle of 2.5 degrees, to either the left visual field or the right visual field. The prime and target exposure duration was 166 ms, while the delay between the offset of the prime and the onset of the target was 250 ms. RESULTS Reaction time and errors were recorded throughout each
block of stimuli. At the end of each block, the mean reaction time of correct responses and error rate was calculated for each Drug Condition (placebo or chlorpromazine), Affect Condition (positive, negative and neutral stimuli), Visual Field (left or right visual field) and type of Word Pair (word-word or word-nonword pair) and these means were used in subsequent analyses of variance. Correct Reaction Times
The mean reaction time of correct responses appears in Table 2. Initially, the reaction times were submitted to a 2 x 3 x 2 x 2 repeated measures analysis of variance with drug, affect, visual field, and word pair as within-subject factors. Gender was not found to be a significant between-subjects factor and so was ignored in further analyses.
A significant main effect for Word Pair was observed, F(1,15)=90.83, p
0031-9384/91 $3.00 + .00
Chlorpromazine and the Lateralisation of the Perception of Emotion L. R. HARTLEY, L. K. IRELAND, P. K. ARNOLD AND J. SPENCER
Department of Psychology, Murdoch University, Western Australia 6150 Received 22 January 1991 HARTLEY, L. R., L. K. IRELAND, P. K. ARNOLD AND J. SPENCER. Chlorpromazineand the lateralisation of the perception of emotion. PHYSIOL BEHAV 50(5) 881-885, 1991.--In a double-blinddesign, sixteen volunteer students were administered 50 nag of chlorpromazineor a placebo in tablet form on separate occasions, two hours prior to testing. The test was a lexical decision paradigm involvingunilateralpresentationof pairs of neutral, positive and negativeemotionalwords and nonwordsto the left or right visual fields. Reactiontime to identify words and nonwords was recorded. Neutral stimuli were processed faster in the left hemisphere, while negative stimuli were processed faster in the right hemisphere. Chiorpromazineimproved speed of response for neutral stimuli presented to the right hemisphere and for affective stimuli presented to the left hemisphere. Thus chiorpromazine seems to benefit right hemisphere processing of nonaffective stimuli and benefit left hemisphere processing of affective stimuli. Chiorpromazineappeared to have a different impact on neutral and affective words, and on the right and the left hemispheres. The general effect of chiorpromazine was to reduce lateralisation.It was suggested that this occurred because chlorpromazine blocked dopamineand possibly other neurotransmitters. Chiorpromazine Word pair
Lateralisation
Emotion
Human
RECENT findings suggest that the processing of not only language (1, 5, 19) but emotional stimuli may be lateralised to the cerebral hemispheres. Several lines of evidence implicate the right hemisphere in processing emotional stimuli. Results of studies of dichotic listening (2, 4, 16), tachistoseopic presentation (15,21), facial expression (18) and hysterical neurosis (8) have all indicated a right hemisphere dominance in the processing of emotional material. In addition, Tucker (23) proposed, on the basis of studies of psychopathologics and unilateral brain damage, as well as normal subjects, that the processing of emotional valence may be lateralised. Such studies suggest that the left hemisphere may be specialized for processing positive affect, as damage in this hemisphere leads to greater expression of negative emotion. In contrast, damage or suppression of the fight hemisphere typically results in a euphoric-manic reaction (20), suggesting the right hemisphere is responsible for processing negative affect. Buck has further suggested (3) that affective information passes from the limbic system to the frontal lobes of both hemispheres, though more directly to the fight hemisphere. Output from the left hemisphere concerns higher order affective processes, such as anxiety, while the fight hemisphere reports on primary emotions (3). Tucker and Williamson (24) have noted the asymmetrical distribution of some neurotransmitters in animal and human brain (11,12). While norepinephrine and 5-HT pathways are lateralised to the fight hemisphere, dopamine pathways are abundant in the left hemisphere, and stimulation of the dopamine
Dopamine
Affectcondition
Visualfield
pathways results in an asymmetric increase in motor function (9). The dopamine system has been shown to have an excitatory influence on motor behaviour (7,14), and may have a role in active attentional processes by coordinating motor output with perceptual information (24). The evidence briefly reviewed above suggests there may be a relationship between affect, hemispheric arousal and dopamine. This study, therefore, examined the lateralisation of the perception of affective words and whether the extent of the lateralisation was influenced by chlorpromazine. Pairs of verbal stimuli were laterally presented to each visual field, and the speed of their perception recorded. Stimuli presented to the left visual field are assumed tO be fast processed by the fight cerebral hemisphere and vice ~ersa for stimuli presented to the fight visual field. The fast stimulus in the pair was a word and the second was either a related word or a nonword. The study required subjects to decide whether the second stimulus was a word or nonword. It was expected that word-word pairs would be responded to faster than word-nonword pairs as words are processed faster than nonwords (6,17). It was also expected that the perception of neutral stimuli would be faster in the fight visual field as the left hemisphere is the prime linguistic processor. If emotion is primarily processed in the right hemisphere (1,16), then it would be anticipated that emotional stimuli would be perceived faster in the left visual field. If chlorpromazine blocks the lateralised dopamine system then the drug should reduce any lateralisation of the perception of emotional words.
881
882
HARTLEY, IRELAND, ARNOLD AND SPENCER
TABLE 1 Word Prime--Word Target
T A B L E 1 (continued)
Word Prime--Nonword Target
Neutral Stimuli Arm--Leg C a m p - - Tent Cat -- Dog Hide--Seek Hour--Time Lark -- Bird Amount-- Money Mother -- Father Q u e e n - King Reflex -- Action Dream -- Sleep Sky--Blue Soil--Dirt Sugar-- Sweet Wigwam -- Indian City --Town Frog--Toad Boat-- Sail Author -- Writer Shoe-- Sock Hint--Clue Aunty--Uncle River--Water Read-- Book Moon-- Star Car-- Bus Bath-- Soap Season--Summer Figure -- Number Head -- Hair Tree--Leaf Paper -- Pencil Plant--Green Hot--Fan Cup--Mug Pot--Pan Letter -- Parcel Bike--Ride A r m y - - Navy Black--White
Arrn--Lig Camp -- Tont Cat-- Rog Hide--Ceek Hour--Tome Lark-- Berd Amount -- Siney Mother -- Futher Q u e e n - Kang Reflex -- Axtios Dream-- Sleop Sky--Brue Soil--Dirl Sugar-- Sweel Wigwam-- Insief City--Toan Frog--Toas Boat-- Saim Author -- Wriser Shoe--Seck Hint--Clum Aunty--Onkle River--Worte Read -- B oak Moon-- Ster Car -- Bas Bath--Stap Season-- Sommer Figure -- Namber Head-- Sair Tree--Leof Paper -- Dencil Plant--Greep Hot--Fon Cup--Mig Pot--Pag Letter -- Parncel Bike--Rime A r m y - - Novy Black--Chite Positive Stimuli
Love--Kiss Joy -- Glee Peace-- Loyal Bride --Bliss Merry-- Happy Laugh -- Smile Adore -- Amuse Lover -- Marry Thrill-- Praise Friend -- Warmth Excite-- Humour Cuddle -- Caress Tender -- Honour Success -- Delight Emotion-- Feeling Romance -- Passion Sensual -- Intense
Love--Kest Joy -- Glea Peace-- Lodal Bride--Brids Merry-Lapsy Laugh-- Spole Adore-- Amose Lover -- Monny Thrill-- Proote Friend-- Wemth Excite -- Hotour Cuddle -- Core st Tender -- Hodoar Success-- Doleght Emotion -- Doesint Romance-- Pestion Sensual-- Ontinze
Word Prime--Word Target
Word Prime--Nonword l'arget
Pleasure--Tranquil Fun--Hug Joyous--Special
Pleasure- Tridsoal Fun--Ric Joyous--Sleciol Negative Stimuli
Cry -- War Death--Ghost Grief--Mourn Drown-- Loathe Devil -- Satan Agony--Cruel Enemy --Panic Corpse -- Scream Suffer -- Misery Murder -- Behead Sorrow -- Funeral C a n c e r - Savage Horror -- Terror Molest-- Malice Kill-- Slay Stab-- Pain Hell -- Hate Despair--Jealous Repulse--Disgust Execute--Torture
Cry -- Wot Death--Grost Grief--Poard Drown -- Goetre Devil -- Jouse Agony-- Snuke Enemy-- Speol Corpse-- Presem Suffer -- Masard Murder -- Somead Sorrow-- Fanotal C a n c e r - Setuge Horror -- Patmar Molest -- Charch Kill -- Ladi Stab -- Deok Hell -- Coud Despair-- Deokous Repulse--Tistere Execute--Gondare
METHOD
Subjects Eight m a l e and eight female university students aged 2 0 - 2 9 years participated in the study. E a c h subject gave i n f o r m e d consent and n o n e h a d a n y health p r o b l e m s , including brain or liver d a m a g e , p r e g n a n c y or illness. Subjects were selected on the basis o f their score o n the E d i n b u r g h H a n d e d n e s s Inventory (5) indicating right h a n d e d n e s s .
Stimuli Stimuli were letter strings c o m p r i s i n g pairs o f w o r d s or nonw o r d s o f 3 - 8 letters a n d 1 - 3 syllables as s h o w n in T a b l e 1. S t i m u l u s pairs were presented on a V D U screen in block capitals lateralised to each visual hemifield. T h e s t i m u l u s pairs consisted o f a p r i m e w o r d followed b y either a related target word (e.g., A R M - - L E G ) or target n o n w o r d (e.g., A R M - - L I G ) o f similar length a n d n u m b e r o f syllables. Prime a n d target w o r d s were d r a w n f r o m the s a m e affective category a n d were E n g l i s h n o u n s in c o m m o n u s a g e and classified according to their e m o t i o n a l c o n t e n t as neutral, positive or negative. E i g h t y neutral w o r d s were selected f r o m the M o n a s h Free A s s o c i a t i o n N o r m s (22) to c o m p r i s e 40 neutral pairs o f stimuli. T e n i n d e p e n d e n t j u d g e s rated 100 positive and 100 negative n o u n s for emotionality. T h e 40 w o r d s rated as m o s t positive and 40 w o r d s rated as m o s t negative were selected to c o m p r i s e 20 pairs o f positive and 20 pairs o f negative stimuli. N o n w o r d s were nonaffective and were c o n s t r u c t e d b y c h a n g i n g one or m o r e letters in a target word to r e n d e r t h e m m e a n i n g l e s s but orthographically legal.
CHLORPROMAZINE, LATERALISATION AND EMOTION
883
TABLE 2 MEANREACTIONTIMES(IN ms) Chlorpromazine
Placebo LVF
Neutral Positive Negative
LVF
RVF
RVF
W
NW
W
NW
W
NW
W
NW
525 518 533
656 670 613
480 573 568
647 639 621
491 519 502
603 615 582
481 505 495
577 606 582
Design
The experiment was a 2 (drug) x 2 (word pair type) × 3 (affect) × 2 (visual field) design with repeated measures on all variables. Two dependent variables, reaction time to correct decisions and number of errors, were recorded. Subjects were administered a placebo and a 50-mg chlorpromazine tablet on two separate occasions two hours before testing under double-blind conditions. Half the subjects received the placebo first, while the other half received chlorpromazine first. Procedure
Each subject was required to attend a practice session a minimum of two days before the first testing session. Testing sessions were scheduled a week apart at the same time of day. Subjects received their tablet two hours before testing. Prior to each testing session, subjects were given 50 practice trials to refamiliarise them with the task. During testing, subjects received 200 trials with 40 pairs of neutral stimuli, 200 trials with 20 pairs of positive stimuli and 200 trials with the 20 pairs of negative stimuli. Stimuli were presented in blocks of 100 trials of each affective class. Equal numbers of word-word and word-nonword pairs were presented in each affect condition. Presentation order of blocks of 100 stimuli of each affective class was balanced by a Latin Square design. Presentation of the different stimulus conditions was also balanced across the visual fields. Throughout the experiment, a fixation dot remained in the centre of the VDU screen. Stimulus pairs were randomly presented, at a visual angle of 2.5 degrees, to either the left visual field or the right visual field. The prime and target exposure duration was 166 ms, while the delay between the offset of the prime and the onset of the target was 250 ms. RESULTS Reaction time and errors were recorded throughout each
block of stimuli. At the end of each block, the mean reaction time of correct responses and error rate was calculated for each Drug Condition (placebo or chlorpromazine), Affect Condition (positive, negative and neutral stimuli), Visual Field (left or right visual field) and type of Word Pair (word-word or word-nonword pair) and these means were used in subsequent analyses of variance. Correct Reaction Times
The mean reaction time of correct responses appears in Table 2. Initially, the reaction times were submitted to a 2 x 3 x 2 x 2 repeated measures analysis of variance with drug, affect, visual field, and word pair as within-subject factors. Gender was not found to be a significant between-subjects factor and so was ignored in further analyses.
A significant main effect for Word Pair was observed, F(1,15)=90.83, p
