PSYC 170  - Summer 2013 - Professor Claffey

Notes: Lateralization



________________ - function is more dependent on one hemisphere (left/right) than the other
contralateral - across/different sides
ipsilateral - same side

Contralateral systems: vision, somatosensory, motor control (not hearing)

Physiological Asymmetries

asymmetrical brain Note: left and right are reversed in the image

Right frontal lobe tends to extend farther forward, Left occipital lobe tends to extend farther back (Galaburda et al, 1978)

Evidence for this asymmetry in 60,000 year old fossils (Lemay, 1976)

Differences in neurotransmitters
    greater dopamine and dopamine receptors in left globus pallidus (basal ganglia) (Glick, Ross & Hough, 1982)
    greater norepinephrine in right thalamus (Oke et al, 1978)
cerebral _____________________

    theory that one hemipshere leads or dominates the other in function
    originated by Hughlings Jackson in 1860s
    oldest, strongest version of the theory was that right hemisphere did little more than sensory processing
    modern view tends to see hemispheres as being specialized/cooperative


    problems with speech
    typically patients with aphasia have damage to ________________ hemisphere
        95% of right handed people have language in left hemisphere (Rasmussen & Milner, 1977)
        left handed people usually have language in the left hemisphere

lateralization language areas
Paul Broca & Carl Wernicke
 - physicians in 1860's
 - performed autopsies on people with aphasia
 - noticed the reliability of damage to left hemisphere
 - earliest evidence for lateralization in the brain

Lesions to Broca's area (Broca's aphasia)
 - difficulties in speech production
 - can still comprehend language

Lesions to Wernicke's area (Wernicke's aphasia)
 - difficulty in comprehending language
 - fluid (but nonsensical) speech production

Broca's aphasia - old, recent
Wernicke's aphasia - old

language heat map

above figure shows area which, if damaged, produced the greatest different between stroke patients and healthy individuals in fluency
    101 stroke patients with left hemisphere damage

Language & the right hemisphere
    Better at identifying prosody (rythym & stress) - emotive content of language
    Cannot understand long/complicated grammatical structures (Zaidel, 1978)
        Can understand basic dichotomies ("The girl stood up" versus "The girl did not stand up")
    Vocabulary is largely limited to concrete words (Zaidel, 1990)
    Unable to identify phonological properties of speech (e.g. identify rhymes) (Levy & Trevarthen, 1977)

Split-brain patients

 ____________________________ can be surgically cut (commissurutomy)
    done either experimentally (animals) or to treat epilepsy (humans)
    effects in human patients are obvious/subtle

In cats (Myers & Sperry, 1953)

cat split brain Details at

Four different treatments in the experiment:
A. no surgery
B. cut the optic chiasm
C. cut the corpus callosum
D. cut both optic chiasm and corpus callosum

One hemisphere learned as fast as both hemispheres still connected

Learning could be transferred across corpus callosum

In humans (Gazzaniga)

split                  brain patients: saying versus speaking
Details at

Patients have corpus callosum cut as epilepsy treatment

Different objects/words could be presented to each hemisphere

Subject could verbally report if presented to the left hemisphere,
   but not to the right hemisphere
Subject could demonstrate object use if presented to
   either hemisphere (Gazzaniga et al, 1962)

2 hemispheres are functioning independently within a person

Videos: Gazzaniga w/ Alan Alda, Other
Wada Test
    used to ___________________________ before brain surgery
    anesthetize one hemisphere of the brain at a time with barbiturate (sodium amobarbital)
    physician knows that the drug has its effect when temporary, contralateral paralysis is observed
    can impair speech in conscious subjects
    modern alternative is to use fMRI (Rutten et al, 2002)


Visuospatial / Object Recognition

warrington 1978
wais block design patients with right hemisphere lesions have difficulty recognizing objects if they are not in their standard form (Warrington & Taylor, 1973)

right hemisphere lesions are impaired at
   matching by perceptual similarity
left hemisphere lesions are impaired at
   matching by semantic similarity
        (Warrington & Taylor, 1978)

left hand can accurately perform WAIS block design task, right hand is clumsy

left hand could draw 2D representations of 3D structures, right has difficulty (Gazzaniga, 1970)

patients with right hemisphere lesions have difficulty judging line orientation (Benton et al, 1975)
left hand is better at feeling an object and matching it to a visual display (Witelson, 1974; Gibson & Bryden, 1983)
    experiment was performed in healthy individuals, examaning two objects simultaneously

Global versus Local

hierarchical figures
right hemisphere damage causes loss of big picture
left hemisphere damage causes loss of local details
(Review: Robertson & Lamb, 1991)

Processing of metaphor, gist and inferences across text are associated with the right hemisphere (Beeman & Chiarello, 1998)


patients with right hemisphere lesions have difficulty
    judging whether they have previously viewed a face (Yin, 1970)
    interpreting emotional expression of faces (Bowers et al, 1985)

    problems initiating movement out of context
        movements in context can be routines that don't rely on cortex
    associated with damage to left hemisphere

    ignoring one side of the body / space / objects
    typically associated with damage to right parietal lobe


lateralization rsa animate
Theory of right for global, left for local
By psychiatrist and writer Iain McGilchrist (full video of lecture)
jill bolte taylor
Narrative experience of stroke in the left hemisphere and what right hemisphere consciousness is like

Copyright 2013 - Michael Claffey