THE HEMISPHERIC SPECIALIZATION OF THE HUMAN
BRAIN AND ITS APPLICATION TO
PSYCHOANALYTIC PRINCIPLES
DAVID A. SCOLA, M.D.
Volumes of research have been accumula ted over th e past decad e concerning
hemispheric specia liza tion of the human brain. Likewi se, over th e past century,
psycho analysts have painstakingly unraveled through their clinical observation ma ny
of the mysteries of intrapsychic functions. Yet little has been wri tt en concern ing
attempts to integrate these seemingly divergent viewpoints.
It was Freud's hope that a neura l basis for his clinical observa tions a nd
psyc hological explanat ions of the human mind would eventually be establ ished . T his
was not possible in his day, however, so this idea was gr adually a ba ndo ned. W ith th e
advent of computers and high technology, perhaps it is time for a reex a min a tion of this
premise. For example, Position Emission Tomography, with its unique a bility to
observe the brain in action via the brain's metabolic utili zation of radioactively labeled
glucose may open as yet und reamed of frontiers in the neurosciences. Th e tec hnologi cal adva nces being used to unlock the mysteries of the brain may a lso be a ble to help
elucidate the secrets of human beh avior.
Indeed, psychiatry has benefited from the technology of the la tt er half of this
century. The wide acceptance a nd usage of psychotropic medications a ttests to this
fact. Yet, dynamic psychiatry and biologi cal psychi atry have very litt le points of
intersection. There seems to be no cross fertilization of ideas a nd methods. This can
only be to the detriment of both practitioners and their pati ent s.
This paper is an attempt to reconcile two seemingly unrelated a reas, i.e.,
hemi spheric speci aliz ation of the hum an brain a nd psychoanal ytic use of dr ea ms, their
interpretation and free association. It is hoped that through the examinat ion of these
well established psychoanalytic techniques that they may be seen in a somew hat
different perspective, the laterality pa radigm. In many ways it echoes tr aditiona l
psychoanalytic concepts a nd may rep resent the neuropsychologica l underpinnings of
what Freud so astutely obse rved abo ut the nature of the human psyche. Hopefully, the
psyc hoanalytic an d latera lity perspectives can mutually enhance each other a nd
through this enhanceme nt , help fu rther unlock an d uncover the mysteries of the hu man
brain and its functioning.
We will initially consi der the function of the cerebral hemispheres in th e hu man
brain both in the ad ult and child. Likewise the role of the corpus callo sum will be
examined, primarily from a developmental per spective. From there, the psychoan a lytic
principles me ntioned above will be discussed.
Dr. Scola is a fo urth-year resident in Psychiatry .
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The Hemispheric Specialization of the Human Brain
3
Brief Overview of Right Hemisphere Properties
The right hemisphere, in general, seems to express itself in a non-linguistic
manner and preferentially processes affective material (I) . The right hem isphere is
also dominant for tactile and proprioceptive sensations (2), orientation in space,
artistic and musical endeavors, body image and recognition of face s. It processes
information more diffusely than does the left hemisphere, being specialized for the
integration of many inputs at once (3). Its mode of operation has been term ed holistic,
relational, simultaneous, and appositional (3 ,4) .
Brief Overview of Left Hemisphere Properties
The left hemisphere is most notable for containing the neural substra te for th e
expression and comprehension of language (Broca 's and Wernicke's a reas respec tively). It specializes in the perception and labeling of material th at ca n be coded
linguistically (5). It organizes and categorizes material into discr ete tempora l a nd
sequential units, processes mathematical and analytical functions a nd med iat es verba l
concept formation (6, 7). Its mode of oper ation has been described as linear ,
sequential, analytical and logical (3).
These function al modes of operation of the cerebral hemi spheres have neuroanatomical correlates. A relatively higher concentration of white matter in the right
hemisphere as compared with the left suggests a gre ater degree of neuronal inte rcon nection (8). This observation supports the suggestion (2) th at the recept otopic
distribution of information across the cortex is focal and discrete in th e left hem isphere
but more diffuse and generalized in the right hemisphere.
The Right Hemisphere and Emotion
Emotionality appears to be most intimately related with subcortica l limbic
structures (9). However, these limbic structures maintain intimate neural connection s
with the right hemisphere. The right frontal a nd temporal region s ar e actually
outgrowths of limbic nuclei and have maintained cytoarchitectural as well as
functional similarities to limbic cortex (10) . One way of determining right frontal lobe
activation is by observation of lateral eye movements as the contralateral front al eye
fields initiate their movement. Many studies (I, II, 12) have used the directionality of
lateral eye movements as indicators of hemispheric activation with Schwartz et. al. ( I)
finding that spatial-emotional questions result in leftward eye movements du e to righ t
frontal lobe activation.
Studies of neurological impairment also support the role of the right hemisphere
in emotion. One study (13) showed that right hemisphere damage impa ired story recall
specifically when the story had emotional content. In another study ( 14) , pati ents with
right or left temporoparietal lesions were asked to judge the content of spoken
sentences and the emotional mood of the speaker; both groups did well on conten t, but
the right lesioned group was significantly impaired in the emotional judgmen t. A
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Jefferson Journal of Psych iatry
deficit in comprehension of emotion in a spea ker's tone of voice was again de monstra ted by Tucker, et. a l. (15), which further showed th at right hemisphere dam age
impaired ability to communicate emotion through tone of voice. It was a lso de monstrated that right hemi sphere damage causes a n indi vidual to have difficult y in
expressing emotion through normal tone of voice inflect ions in every day interact ions
(16).
The sa me results have been obt ained with norm al college st uden ts (17 ). A task
requiring judgments of sentence content and the spea ker's tone of voice was ad ministered monaurally via the right or left ears (most input is processed by th e contralat eral
hemisphere). A left ear superiority for the emotional judgm en ts was inter preted as
further indication of the right hemi sphere's importance to affective comprehension.
The right hemisphere also seems to evaluate emotional events nega tively. One
study (18) presented motion pict ures to the visual half-fields through th e use of special
contact lenses. Films prese nted to the left half-fields were rated more negat ively.
Another st udy (19) examined affective responses to TV program s. Front al lobe EEG
record ings showed a differen tia l effect with left frontal activation during positive
affect and righ t fro ntal activation d uri ng negative affective responses. In ano ther stu dy
(20) subjects generated tho ughts, feelings or images associated with positive or
negative experiences. The results again showed preferential right fronta l activation for
negative experiences and left frontal activation for positive ones.
A remarkable case st udy (21) illustrates the negativeness tha t th e right
hemisphere may possess. A 12-year-old right-handed epileptic boy who was a lso
bilingual was commissurotomized (surgical sectioning of the corpus ca llosu m) at age
II for intractable seizures. One test required him to rate words on a goodness-badness
scale with 1 representing good and 7 representing bad. The right hemi sphere
consistently rated words worse than the left. For exa mple the word Moth er was rat ed 1
by the left and 6 by the right hemi sphere. Sex received th e sa me ratings. On the tes ting
day described above , the subject' s affect was anxious and he was genera lly " hyperactive and aggressive" (not further described). On a nother testing day when th ere was
very little left-right discrepancy of word evaluations, the subject was descr ibed as
" ca lm, tracta ble and appealing." Thus, negative behavioral a nd mood chan ges were
accompanied by a left-right hemisphere discordancy. The right hemi sphere seemed to
be in a bad mood. In this subject, therefore, the right hemi sphere was intimately
involved with nega tively rated, emotional material. Except for the last menti oned study
all previo usly men tioned references pertained to adults.
Laterality in Children
Many of the studies of la tera lity in children parallel those of adults. Long before
lang uage skills have developed there is a n asymmetry of electrical cortical responses to
verbal a nd non-ver bal stimuli. A study (22) found that newborns (m ean age = 5.8
onths) showed a greater electrical activation over the left hem isphere in response to
verbal stimuli while non-verbal stimuli (a musical chord) resulted in gr eater right
hemisphere activation . These findings were replic ated (2 3) for 3- a nd 4-mont h-old
The Hemispheric Specialization of the Human Brain
5
infa nts. Battro (24) found logica l a nd spatia l opera tio ns (as measured by Piageti an
tes ts) to be laterali zed in opposite hemi spheres in children 4-8 years of age. Righ t
hem isphere speciali zation for tactil e-spat ial processing in 4- an d 5-year-olds were
found (25) in a n experiment involving the visua l recognition of sha pes haptically
explored by either hand . Mor eau a nd Milner (2 6) found a right hemisphere superiority
in 5-year-olds for identifi cation of unil atera l, bilateral a nd doubl e simultan eous
ipsilate ra l and contralateral tactile stimulation of the face and hand s. Ingra m (27)
studied children 3-5 yea rs of age a nd found th at th e left ha nd (right hemi sph ere )
performed better a t hand posture a nd finger spacing tasks. C hildren of ages 5, 7 and I I
yea rs were found to have a right hemi sphere superiority in the visual recognition of
face s presented briefly to the right or left visua l field (28). A litera ture sea rch revealed
only one study pertaining to emotional stimuli in infa nts a nd ch ildr en. A study of
IO-month-old infants showed gre ater left front al activati on when shown a videot ape of
a n actress generating a happy face . No difference was found betw een the hem ispheres
in the front a l regional in response to sad stimuli (actress genera ting a sad face) .
In adults, the right hem isphere seems to preferentially process negat ive affective
stimuli, while the left hemi sphe re is more activated with positive affec tive sti muli. Onl y
the latt er seems to be true in this study of 10-month-old infan ts. Mu ch more data a re
needed , however, and thi s a rea seems to be one which requ ires much more resea rch.
The Corpus Callosum in Children
The corpus callo sum is the neural structure th at principall y mediates the
interhemi spheric tr an sfer of information. The a nte rior commissure funct ions in th e
sa me manner but to a much lesser extent. Apparentl y th e cor pus callosum is one of the
last systems to begin a nd to compl ete myelination. In hu man s, myelination does not
begin until th e end of th e first yea r (30), is substa ntia lly adva nced by age 4, lar gely
completed by age 6, a nd continues to slowly myelinat e until a t least age 10 (31) . Thi s
a natomical imma turity is par alleled by functi onal imm aturity.
Galin et. al. (30) concluded th at 3-year-olds have more difficulty com pa ring
tactile information between the two hemi spheres th an with in a hem ipshere a nd that
this difference is redu ced by th e age of 5. Jo seph a nd colleag ues (32) found
interhemispheric communication to be so poor that when pictorial stimuli a re
presented tachistoscopically to the right hemi sphere, children 4 yea rs of age will
respo nd when questioned, with large information gaps which th ey erroneously fill with
confa bulatory responding. It th us appears that the left hemi sphere of a young chi ld
has, at best, incomplete knowle dge of the contents and acti vity that occur in the righ t
(33) .
From what has so fa r been discussed, it seems th at in childhood, man y experiences
a re preferentially proce ssed in the right hemi sphere. However with poor lan guage
refinement in the infant and child, man y such experiences a re difficult to remember as
the y were either not ver ball y encoded a t a ll or onl y crudely so. In addition to th e
problem of encodernent, a nother significant impediment to childhood rem emb ra nces is
the poor interhemispheric communication.
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Jefferson Journal of Psychiatry
Left Hemispheric Ignorance of Right Hemisphere Cont ents
Wh at is the fate of a memory encoded in a non-verbal man ner ? A carotid amy tal
study (34) can perh aps be helpful in a nswering thi s que stion. The pat ients involved in
this study were being evaluated for suspected tumors and ranged in age from 38-64.
Prior to angiography they were injected with 100-150 mg of 10 percent sodium
amobarbital into the left common carotid artery and approxima tely two minutes later
were presented an object (out of view) to actively palp at e with their left hand .
Immediately after palpation, none were able to name the object (a s was expected since
the left hemisphere was drugged and thus the speech centers inactivated). After the
drug effects had subsided, none of the patients could verb all y recall the tactile
stimulus. Seventy-five percent, however, were able to immediately recogn ize the
correct choice in a visual multiple choice test and usually did so by point ing with the
left hand. This study seems to indicate the difficult y of the adult brain to verbally recall
a n experience encoded in a non-verbal manner. Thi s type of finding has also been
demonstrated in split-brain experiments i.e., in patients who underwent cereb ral
commissurotomy for treatment of intractable seizures (35) . A nude pin-up was flashed
tachistoscopically to the right hemisphere of a female patient with a split-b rain. She
blushed and giggled immediately afterwa rds. When asked what she saw she repl ied
that she only saw a flash of light and continued giggling. When aga in as ked why she
was giggling, she just replied that Dr. Sperry had "s ome machine." Anot her pat ient
was having great difficulty performing a block design task with his right hand (left
hemisphere). In trying to match a corner of the design, the right hand corrects one of
the blocks , and then shifts it again, apparently not reali zing it was corr ect. T he left
hand (right hemisphere) darts out, grabs the block and restores it to the correct
position. Thus in all of these situations, the right hemisphere had acce ss to information
that the left did not. Again, this seem s to be analogous to the situa tion in childhood
discussed above.
Relative Right Hemisphere Autonomy
There is sugge stive evidence from the previousl y mentioned study by Le Doux et.
al. (21) that the right hemisphere has a mind of its own. It was found tha t in this
commissurotomized patient, the right hemi sphere has a sense of self for it knows its
name. In response to further questioning it was found that the right hem isphere has
feelings and a sense of the future, for it can describe its mood and knows what day
tomorrow is. It has aspirations and goals for the future, for it can descr ibe its
occupational choice (which by the way, differed from the left hem isphere response).
It thus seems compelling in view of these studies, to postulate th at within all of us
exist two repositories of experiences and memories which can influence beha vior and
judgment. In essence, there seem to be two minds in us.
Dreams
Since 1953 when Aserinsky and Kleitman (30) first discovered the EEG evidence
of different sleep stages, REM sleep has been associated with dreaming. Th e mode of
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The Hemispheric Specialization of the Human Brain
7
cognition in dreaming is usually of the primary process type; mainl y non-verba l imag e
representations, and violations of ordinary temporal sequencing (37) . Fenichel (38 )
states that primary process thinking is carried out more through pictor ia l, concrete
images, whereas the secondary process is based more on word s. Bogen (4, 39) is of the
belief that the right hemisphere uses a non-verb al mode of represent ation, utilizing
image s, a nd th at the right hemi sphere reasons by a non-l inea r mode of association
rather than by syllogistic logic. It seems, then, th at th e right hemisphere mode of
functioning and the phenomenology of dre ams have much in com mon.
This commonality is further seen in studies of brain-injured pati ent s. O ne study
(40) described three patients who spontaneously reported cessa tion of dreaming
following right posterior brain injuries. Impaired visual imagery in the waking state
was also found. In this reference, four other cases in the older neurologica l literature
are cited in which depression of dreaming and waking visual ima gery were associated
with right parietooccipital lesions. This cessation of dre aming a ppea rs in split-brain
patients also (4). Several of these commissurotomi zed patients report ed that they no
longer had any dreams, in contrast to frequent vivid dre aming before th e operation.
One way of interpreting thi s curious finding is th at if the right hemisphere is the source
of dreams, the left hemi sphere would be unable to verball y report the dr ea ms. since it
no longer had access to them. Hoppe (4 1) found that " .. . pa tien ts after commissurotom y reveal a paucity of dr eam s, fantasies, a nd symbols. Th eir dre a ms lack the
cha racteristics of dream work; their fantasies a re unim agina tive, utilitar ia n, and tied
to reality."
EEG a nd cerebral blood flow finding s (42) seem to indicat e a right hemisphere
domin ance for REM sleep. Other studies (43, 44) have found evide nce of hemispheric
dissociation during REM sleep, resu lting in a functional disconn ection between the
hemisph ere s. This situa tion is a nalogous to th at previously described for young
children, th at the left hemi sphere seems to have impaired access to the contents of the
right both in the dream sta te a nd in childhood. Th is may acco unt for the difficulty that
man y people seem to have in reme mbering their dr eam s. Some, in fact , absolutely
insist th at they never dream. Cohen's dat a (45) suggest a n increase in left hemisphere
participation in dre am experience later in the night. Perhaps this may acco unt for the
observation that many dreams that a re remembered seem to occu r in th e early morning
hour s just prior to awakening.
But what of dream interpretation ? How is this to be understood in th e context of
cere bral laterality? If one views the right hemi sphere as the repository of nega tive
affectively tinged memories that may be difficult to verb ally encode , a nd even more
difficult to communicate interhemispherically (in children at least) , a nd that these
memo ries may influence attitudes and behavior, then perh aps a n explanation can be
attempted. O ne of the main goa ls of psychoanalysis as put forth by Freud was making
the unconscious conscious. If viewed in this way with the right hemisph ere as the rough
equivalent of the unconscious, a nd the left hemi sphere as equivalent to th e conscious
then it seems that some sense can be made of dre am interpretati on in th e context of
cerebr al laterality. The dream becomes the expression of right hemisphere mentation
which largely conc ern s itse lf with the types of memories descr ibed a bove. Insofa r as
present da y event s resonate with affectively ting ed memories of a n earlier time, the y
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Jefferson Journal of Psych iatry
are incorporated as day residue. Yet both in the dream and in th e childhood origins of
the memories which form the basis of the dream , there is little int egrati on with the left
hemisphere, which is still largely ignorant of the contents. Through the associations to
the visual imagery of the dream in a systematic, verbal manner, the unconscious
becomes conscious, i.e., the left hemisphere has further access to the memories that it
previously was largely unaware. Through the combined efforts of both a na lyst a nd
patient, it is as if a right hemisphere memory or experience is ex truded a nd placed
under the scrutinizing gaze of the left hemisphere. In this manner, interhem isph eric
communication is enhanced . The very situations which largely contributed to th e left
hemisphere's ignorance are overcome viz: I) lack of verbal encodement, 2) poor
interhemispheric communication. The affect must become integrated with th e logic.
But what about free association . Can it too be understood in this context ?
Free Association
Free association is the fundamental rule of psychoanal ysis. It involves "a
particular condition of mind, one which approximates an intermediate state bet ween
sleep and wakefulness in which judgmental faculties are held in abeyanc e a nd thoughts
flow in the form of fantasies and pictorial images. It . . . indicates closen ess to th e type
of thi nking that exists in the unconscious" (46). From what has beeen previously sta ted
in this article, "judgmental faculties" can be taken as a left hemisphere function while
pictorial images are mediated by the right hemisphere. It has also been found th at the
seemingly haphazard associations are actually connected via affect, not logic. In other
words , the right hemisphere appears to be intimately involved in the production of free
associations if the roles of the hemispheres as presented in this paper ar e followed . To
the best of my knowledge, there have not been any EEG studies of people undergoing
the free associative process. However, a closely related state has been examined , viz.,
meditation. The techniques of meditation seem to be designed purposely to avoid
logical, verbal and rational reactions to perceived events. Sustaining attention on one
object as in one-pointed concentration, naming or noting stimuli successively as they
enter consciousness as in Buddhist mindfulness (the similarity to free associa tion is
striking), and maintaining a visual mode of imagery combined with concentrat ion as in
tantric practice, all appear to reduce abstract thought and verb al associations (47) . If
attention is a right hemisphere mediated function as Mesulam and Geschwind (48)
contend, then it, along with visual imagery and the avoidance of verbal logic a nd
rationality, seem to indicate that in meditative techniques the left hemisphere is
switched off and the right hemisphere is turned on. Both Glueck and Strobel (49 ) a nd
Erlichmann and Wiener (50) have EEG evidence to this effect. Their data suggest that
the initial stages of meditation (the first one to two minutes) are associated with
greater deactivation of the left hemisphere and hence a relative right hemisphere
dominance.
As Sloane (46) points out, a mere flow of words in a stream-of-consciousness style
cannot lead to understanding. Free association must be combined with self-observation
and interpretation. In other words, free association is a dynamic active process in the
The Hemispheric Specialization of the Human Brain
9
sense that the products of the associative proce ss tha t a re ar rived at in a relaxed sta te
a re subjected to a more active, inten sive scru tiny in the self-observing and interpreting
process. Thi s leads us to a similar conclusion as the one that we arrived a t when we
examined dreams in the cont ext of cerebral lat erality, viz., that right hemisphere
ment at ion is actively examined by the a na lytic left hemisph ere (or observing ego), a nd
in thi s way interhemispheric communicat ion is enh an ced a nd the unconscious becomes
conscious .
Another area that may be fru itfully exam ined via the la terality pa radigm is that
of defen se mechanisms of the ego. The female patient of Dr. Sp erry's who blushed at
the tachistoscopically presented nude picture (35) migh t be sa id to be den ying or '-repressing if viewed psychod ynamically. Is splitt ing th e result of impaired interhemispheric communication where the right hemisphere influence s the bad view and the left
hemisphere the good one ? Are isolation of a ffect a nd inte llectua lization, defenses
commo nly used by the obsessive-compulsive, also a result of poor inte rhemispheric
communication? A few studies have attempted to a nswer these qu estions. G ur & Gu r
(II) found that subjects who characteristicall y looked to the left (right hemisphere
activation) in response to questions scored higher on a defen se mech an ism cluster tha t
included repression a nd denial. In a study of hysterical a nd obsessive-compulsive
personalities (51) there was significantly more left looking a mong the hysterical
subjects. Stern (52) found that both right-handed a nd left -hand ed pa tients experi enced a higher proportion of left- sided conversion symptoms (wea kness, par alysis,
sensory loss or numbness) than would be expected by cha nce. Th ese findings a re
intriguing and point to dir ections for future resear ch .
Man y questions rem ain unansw ered a nd it is hoped that psychodyn amic theory
will utilize the insights obtained through the technological , neu rologica l and biological
a pproaches to the study of hum an behavior. In this way, perh aps we can better
understand the child with in the man.
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