1. Human Neuropsychology,
Bryan Kolb & Ian Q. Whishaw’s
Fundamentals of
Human Neuropsychology,
Sixth Edition
Chapter 11
Lecture PPT
Prepared by Gina Mollet, Adams State College

2. Cerebral Asymmetry

3. Portrait: Words and Music
M.S.
Lifetime history of epilepsy
Had a cyst removed from her left temporal lobe
Developed an infection that damaged the left hemisphere
Diagnosed as a global aphasic, but could still sing songs she had known before

4. Anatomical Asymmetry in the Human Brain
Laterality
Left and right hemispheres have different functions
Left hemisphere
Language
Controlling movement on the right side of the body
Right hemisphere
Perceiving and synthesizing nonverbal information
Controlling movement on the left side of the body

5. Anatomical Asymmetry in the Human Brain
Four variables that complicate laterality research
Laterality is not absolute
Cerebral site is just as important as cerebral side
Laterality is affected by environmental and genetic factors
Laterality is exhibited by a range of animals

6. Anatomical Asymmetries
Right hemisphere is larger and heavier than the left; it contains more gray matter
Temporal lobes have a marked asymmetry
Planum Temporale
Larger in the left hemisphere
Heschl’s gyrus
Larger in the right hemisphere
Asymmetry in the temporal lobes correlated with asymmetry in the thalamus

7. Anatomical Asymmetries
Slope of the lateral fissure is gentler on the left hemisphere
The frontal operculum is organized differently on the left and right sides
Distribution of neurotransmitters is asymmetrical
Right hemisphere extends further anteriorly; the left hemisphere extends further posteriorly
Anatomical asymmetries affected by sex and handedness

10. Neuronal Asymmetry
Neurons in the left frontal operculum and in the left precentral cortex have more dendritic branches than those in the right frontal operculum and right precentral cortex

12. Genetic Asymmetry Tao Sun and colleagues
Genes are expressed differently in the right and left hemispheres
May regulate the production of growth factor
May account for functional properties (i.e. handedness)‏

13. Asymmetry in Neurological Patients
Double Dissociation
Two areas of the cortex are functionally dissociated by two behavioral tests
Each test is affected by a lesion in one zone but not in the other
Example: left hemisphere lesions produce language deficits that do not appear after right hemisphere lesions

15. Asymmetry in Neurological Patients
P.G.: Left temporal lobe tumor
S.K.: Right temporal lobe tumor

17. Patients with Commissurotomy
Surgical procedure of severing the corpus callosum
Two hemispheres can no longer communicate
Split-brain
Sensory information is sent to only one hemisphere
Example vision: Input from the left visual field is sent only to the right brain and input from the right visual field is sent only to the left brain

20. The Split-Brain Phenomenon

21. The Split-Brain Phenomenon
Illustrates the right hemisphere’s role in facial recognition
Jere Levy
Split brain patients identify the face that is seen by the right hemisphere

23. Brain Stimulation Effects of applying electrical current to the cortex
Localized movements, localized dysthesias, light flashes, or buzzing sensations
“Interpretive” and “Experiential” responses
Production of déjà vu, fear, dreaming states, visual or auditory memories
Acceleration of speech production
Stimulation can block function if the subject is engaged in an ongoing task

25. Carotid Sodium Amobarbital Injection
The Wada Test
Injection of sodium amobarbital to produce a period of anesthesia in one hemisphere
Allows for the study of each hemisphere
Useful for determining lateralization of speech

27. Behavioral Asymmetry in the Intact Brain
Asymmetry in the Visual System
Tachistoscope can be used to present information to each hemisphere independently
Infer which hemisphere is better at processing certain types of information by looking at accuracy of identification in each visual field

28. Behavioral Asymmetry in the Intact Brain
Asymmetry in the Auditory System
Dichotic listening
Simultaneous presentation of two different stimuli to the left and right ears
Subjects are asked to report which stimulus they heard most clearly
Studies find a:
left ear advantage for music and stimuli with a tonal quality
right ear advantage for verbal stimuli

29. Dichotic Listening

30. Behavioral Asymmetry in the Intact Brain
Asymmetry in the Somatosensory System
Subjects are blindfolded and then asked to perform various tasks with their hands
Differences in efficiency are evidence of lateralization of function
Braille read more rapidly with the right hand
Dichaptic Test
Subjects feel objects and then identify those that they touched
Right hemisphere advantage for shapes; left hemisphere advantage for letters

32. Behavioral Asymmetry in the Intact Brain
Asymmetry in the Motor System
Apraxia - severe deficits in copying sequences of movements
Appear after left-hemisphere lesions
Direct Observation
Watch subjects performing different tasks to see which hand is more active
Wolf and Goodale
Right side of the mouth opens wider and more quickly for verbal and nonverbal tasks
Onset of facial expressions sooner on the left side of the face

34. Behavioral Asymmetry in the Intact Brain
Asymmetry in the Motor System
Interference tasks
Simultaneous performance of two tasks
Example: playing the piano and speaking

35. What Do Laterality Studies Tell Us about Brain Function?
Behavioral studies may be measuring more than just laterality
Laterality studies provide correlations between anatomy and behavior
Measures of laterality are not concordant
Robert Efron
Laterality can be explained by the way the brain “scans” sensory input

36. Neuroimaging and Asymmetry
Reveal activation in the left hemisphere in Broca’s area and Wernicke’s area when speaking and listening to speech

38. Theoretical Arguments: What is Lateralized?

39. Specialization Models
Kimura
Left hemisphere may be specialized for some kind of motor control, rather than verbal functioning
Two hemispheres process information in different ways
Left: Logical, analytical, computer-like fashion, analyzing stimuli sequentially
Right: Overall stimulus configuration, organizations and processes as gestalts

40. Interaction Models
Two hemispheres function simultaneously, but work on different aspects of processing
Two hemispheres have the capacity to perform a given function and they inhibit each other’s activity
Information processing models

41. Snapshot: Imaging the Brain’s Plasticity
Holloway and colleagues
Investigated sensorimotor function in hemispherectomy patients
Found that the passive movements produced activation in areas of the brain that normally respond to the opposite side of the body

43. Preferred Cognitive Mode
Preference of one thought process to another
Left hemisphere people
analytical, logical, verbal, and meticulous
Right hemisphere people
concerned with organizing concepts and visualizing meaningful wholes
Cognitive set
Tendency to approach a problem with a bias
Can affect tests of lateralization

44. Measuring Behavior in Neuropsychology
Results can be difficult to replicate
Numerous ways to measure the same thing
Sometimes multiple measurements may be needed
Example: Foot measurement studies