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1.Specialized Functions of right and left hemispheres

LEFT HEMISPHERE

- right handed people ( left hemisphere is dominant since it controls both language and skilled hand movements

- control of contralateral primary cortical functions (motor control, sensory modalities such as fine discrimination of contralateral body); perception of right visual field

- entire Perisylvian region ( lateral sulcus) of left hemisphere is important for language; posterior lesions disrupt language comprehension (Wernicke’s) and anterior lesions disrupt language production (Broca’s) area; aphasia is the general term of loss of language function

- language comprehension (auditory/syntax); language production (spoken/written); reading aloud (repeating spoken language)

- mathematical skills (arithmetic/calculation)

- sequenced motor tasks

RIGHT HEMISPHERE

- left handed people ( language may be in right, left, or bilaterally represented

- control of contralateral primary cortical functions (motor control, sensory modalities such as fine discrimination of contralateral body); perception of left visual field

- visuo-spatial perception and higher order visual processing; drawing skills (copying); mental manipulation of 3-D structures; special function of facial recognition

- awareness of external spatial world for both hemispheres

- language capabilities: prosody (emotional content of spoken language), noun recognition

- music; more skilled musicians tend to have greater representation in left hemisphere

6. Hemispatial Neglect

- massive damage to right hemisphere (in territory supplied by the right middle cerebral artery)

- patient develops a left hemiparesis due loss of the motor control regions of the right hemisphere; patient does not realize that the left side is impaired; patient may completely neglect everything in the left side of the world

- patient can perceive sensory info, visual info, and auditory info for left side, but simply cannot pay attention to these areas

- loss of right hemisphere function ( hemi-spatial neglect on left; following damage to right hemisphere ( left hemisphere manages its own responsibility for the right spatial world, however it can not take over the function of the right hemisphere ( left hemi-spatial neglect

- right hemisphere is master hemisphere responsible for visuo-spatial processing; left hemisphere is limited

- stroke in left hemisphere ( master function of right hemisphere compensates and takes over the damaged left hemisphere’s role ( no heme-spatial neglect on right (right hemisphere able to assume function for both halves of the world)

2. Executive functions of frontal lobes

- brain uses multiple strategies simultaneously in arriving at a solution for a difficult problem or making complicated decisions calling into play various subsystems as needed; this scenario is true for the frontal lobes who job is the executive functions of the brain: planning, problem solving, social skills

- theoretical problem-solving, personality, long-range planning, socialization, humor, higher order emotional processing, control of other brain regions

- damage to right lobe ( personality disturbance

- damage to left lobe ( depression\

- bilateral damage ( patient does not care about normal basic activities

- frontal lobe damage ( return of reflexes suppressed by frontal lobes after infancy (grasp reflex, snout reflex, glabellar reflex) and perseveration (constant repetition of a response)

3. Apraxia

- loss of ability to perform complex, highly sequenced motor skills

- examples: putting on a shirt, buttoning, steps in smoking a pipe, using scissors

- area responsible for sequenced movements is left hemisphere (left parietal lobe ( motor sequences that require manipulation of objects in space because this is where visual and somatosensory information converges to make cortical maps of the external world)

- Apraxia can be differentiated from weakness and loss of coordination because apraxia patients have normal strength, speed and power of movements, but cannot carry out a motor sequence; in some severe apraxias ( patient cannot even verbalize the steps necessary to perform a sequence or make an attempt to carry out the task (ideational apraxia)

4. Disconnection syndromes

Alien Hand

- can occur following a stroke which damages the supplementary motor area of left hemisphere along its corpus callosal connections to the right hemisphere

- left hand (right hemisphere driven) may act on its own without input from the dominant left hemisphere; engage in exploratory behavior on its own under direction of the right hemisphere

Alexia without agraphia

- left occipital cortex damaged along corpus callosal connections to right hemisphere

- patient cannot read, but can write; patient may write something down and not be able to read it

- damage to left occipital cortex gives rise to right hemianopia; problem not caused by this

- material read in left visual field ( info transferred across corpus callosum where language processing occurs in the left hemisphere (normal)

- alexia without agraphia ( transfer of info from functioning right occipital cortex (left visual field) cannot cross over to language-competent left hemisphere

- verbal output by language areas of left hemisphere can be translated into writing via connection to the motor cortex

5. Angular gyrus syndrome

- angular gyrus of left hemisphere important for arithmetic calculation

- syndrome consists of acalculia (cannot perform arithmetic calculations), finger agnosia (can’t name individual fingers of each hand), right-left confusion, dysgraphia (inability to write)

- associated alexia (inability to read) ( angular gyrus occupies an anatomical location where there is a confluence of information flowing from visual cortex toward language areas of posterior perisylvian regions (supramarginal gyrus)

- reading integrates visual info with language functions

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