Brain Asymmetry and Lateralization of function Lateralization means the cerebral hemispheres are specialized for different functions. Language spatial However, no evidence supports notions that personality traits, creative or analytical thinking are linked to one hemisphere or the other. Hemispheric specialization may have originated in differential use of limbs. Powerful throwing, as in hunting, involved the right hemisphere left-hemisphere circuits needed to program throwing may have begun to control language Other vertebrates also show preference for one limb or the other, so lateralization may have evolved for processing efficiency.

The Left Brain Is Different from the Right Brain Handedness Left-handed people make up about 10–15% of the population. Left-handed children do not differ from right-handed children on any measure of cognitive performance. Handedness may have a genetic component, but if so, it is not a simple, single gene effect. One gene that may contribute to handedness is LRRTM1, a gene associated with glutamate neurotransmission that is also implicated in schizophrenia. Many genes related to handedness some of which regulate body symmetry

Figure 19.1 Testing a Split-Brain Individual Hemispheres communicate with each other so quickly, lateralization of function is masked. Sperry’s studies tested language function in each hemisphere of split-brain individuals. Split-brain individuals’ hemispheres are disconnected due to the surgical severing of the corpus callosum to alleviate seizures. Words presented to either visual field showed language ability only if the information reached the left hemisphere. Figure 19.1  Testing a Split-Brain Individual Words or pictures projected to the left visual field activate the right visual cortex. (A) In intact individuals, activation of the right visual cortex excites corpus callosum fibers, which transmit verbal information to the left hemisphere, where the information is analyzed and language is produced. (B) In split-brain individuals, stimuli from the left visual field reach the right-hemisphere visual cortex via the subcortical visual pathways (they are independent of the corpus callosum). However, the split corpus callosum prevents right-hemisphere visual areas from communicating with the language areas of the left hemisphere, so verbal responses to the stimuli are impossible (left). In contrast, split-brain individuals are able to respond verbally to stimuli appearing in the right visual fields, because interhemispheric transfer is not required (right).  

Figure 19.3 The Right-Ear Advantage in Dichotic Presentation A dichotic presentation delivers different stimuli to each ear at the same time. Right-handed persons identify verbal stimuli delivered to the right ear more accurately than verbal stimuli delivered to the left—a right ear advantage. 50% of left-handed individuals have a left-ear advantage. The right ear advantage may reflect the left hemisphere’s specialization for language. This advantage is only evident in simultaneous presentations and is restricted to consonants. Figure 19.3  The Right-Ear Advantage in Dichotic Presentation (A) A word delivered to the left ear results in stronger stimulation of the right auditory cortex. (B) A word delivered to the right ear results in stronger input to the left hemisphere. (C) When words are delivered to both ears simultaneously, the word to the right ear is the one usually perceived because the right ear has more-direct

The Left Brain Is Different from the Right Brain The right hemisphere is specialized for: Processing emotional tone of language Prosody: the patterns of stress and intonation in a language Perception of music Controlling attention Spatial processing, including: Face perception Geometric shapes and relations Direction and navigation 3D rotation of imaginary objects

Figure 19.5 Use of the Right Hemisphere for Facial Recognition Anesthetizing the left hemisphere in a Wada test (see Box 19.1) does not interfere with a participant’s ability to recognize her own face in a picture that is a composite of her face and the face of a celebrity. But when the right hemisphere is anesthetized, the participant interprets the composite face as that of the celebrity. Figure 19.5  Use of the Right Hemisphere for Facial Recognition Anesthetizing the left hemisphere in a Wada test (see Box 19.1) does not interfere with a participant’s ability to recognize her own face in a picture that is a composite of her face and the face of a celebrity. But when the right hemisphere is anesthetized, the participant interprets the composite face as that of the celebrity. (From Keenan et al., 2001, courtesy of Dr. Julian Keenan.)

Right-Hemisphere Damage Impairs Spatial Cognition Prosopagnosia can result from brain damage (acquired prosopagnosia) congenital prosopagnosia—lifelong face blindness not due to brain damage—occurs in about 2.5% of the general population. Bilateral damage to the fusiform gyrus causes complete prosopagnosia. located in the Inferior temporal cortex part of the visual ventral stream Prosopagnosia may be accompanied by other forms of agnosia, an inability to identify items such as different kinds of cars or species of birds. On the other hand, some people are “super-recognizers.”

Reading Skills Are Difficult to Acquire and Frequently Impaired Dyslexia: A reading disorder attributed to brain impairment. Acquired dyslexia (alexia) can occur in adults after injury to the left hemisphere. Deep dyslexia is an acquired dyslexia in which a person reads a word as another semantically related word. Surface dyslexia, another acquired dylexia, the person attends only to the fine details of reading—which letter makes which sound. Surface dyslexics find it difficult to recognize words in which the letter-to-sound rules are irregular. Developmental dyslexia occurs in 5% of the general population.

Figure 19.19 Neural Disorganization in Dyslexia (Part 1) Brains of dyslexics show unusual arrangements of cortical cells. Micropolygyria - small regions of excessive number of gyri or cortical foldings Ectopias - clusters of cells in unusual places Dysplasia - loss of characteristic architectural organization of the cortical neurons, mainly subjacent to the site of ectopias Figure 19.19  Neural Disorganization in Dyslexia (A) (Top) Drawings of the left and right planum temporale (see Figure 19.4) from the brain of a person with dyslexia show these regions as nearly symmetrical; in most people the left planum temporale is considerably larger. The dots and the shaded area represent regions where microscopic anomalies called ectopias, dysplasias, and micropolygyria have been found in the brains of individuals with dyslexia. (Bottom) Anomalies in individuals with dyslexia are much more common in the left hemisphere, which is primarily responsible for language function. (B, C) These micrographs show (B) micropolygyria (literally “many tiny gyri”) and (C) ectopias, clusters of neurons in unusual locations, such as this cluster in cortical layer I (arrow), which is normally devoid of neuronal cell bodies. (After Galaburda, 1994; micrographs courtesy of Dr. Albert Galaburda.)

Social Cognitive Neuroscience An approach that has its roots in Social Psychology and borrows heavily from Cognitive Psychology procedures and theory A combination of social paradigms, cognitive tasks and neuroimaging Studies how individuals process social information Person perception – how you perceive individuals and Attribution – nice person bad person Attitudes – likes and dislikes Prejudice and Stereotyping Judgment of others behavior Memory of social stimuli Studies effects of social and affective factors on information processing Not just cognitive psychology in a social context because “people are not things”

Evolution of Social Cognition Dogs but not other canines Track body movements Track eye gaze Follow pointing gestures Non human primates Non verbal communication Cooperation in small social groups Transmission of Culture within the group Evolution of large brains in primates computational demands of living in large, complex societies particular demands of the more intense forms of pair bonding Role of language in humans Gossip is the most important use of language

Social Cognitive Neuroscience Frontal lobes injury can adversely affect social judgments Example of Phineas Gage Many other examples from Neurology Psychological processes that promote social behavior Non-verbal communication Verbal communication Face recognition Body shape preferences Moral judgment and Fair play Cooperation Keeping track of social relationships Mind Reading “theory of mind” Specialized circuits for social cognition Are cognitive processes for perception, language, memory and attention sufficient to explain social competence? are there specific cognitive processes that are special to social interaction?

Social Networks In The Brain social networks of friends and family understanding the social relationships allows us to interact with them appropriately to maintain social networks requires keeping track of our relationships to others and some understanding of their relationships to one another fMRI studies of participants while they viewed film clips of individuals within this social network their friends, some were friends of their friends and some were friends of their friends’ friends (two vs. three degrees distant) distributed network of brain regions was sensitive to the social status familiarity and social distance are processed in the inferior parietal lobule socially relevance of other people is processed in the medial prefrontal

Thinking about other people Theory of mind “mentalizing” attribute mental states to other people representing what might be going on in other people’s minds emerge at about four years of age and may be unique to humans Ability to see the world from another’s perspective tracking eye-movement and using their visual perspective posterior end of the superior temporal sulcus (pSTS) and the adjacent temporo-parietal junction (TPJ) Thinking about mental states activates medial prefrontal cortex and adjacent paracingulate cortex anticipating what a person is going to think and feel predict what they are going to do based on past experience of interacting with others based on personal experience in similar situations