Higher Cortical Function

Transcription

1 Emilie O Neill, class of 2016

2 Higher Cortical Function Objectives Describe the association cortical areas processing sensory, motor, executive, language, and emotion/memory information (know general location instead of numbers) Describe the effects of lesions to the above cortical association areas including agnosia, apraxia, neglect, and aphasia. Understand the concept of hemispheric dominance and its relationship to language. Chris Cohan, Ph.D. Dept. of Pathology/Anat Sci University at Buffalo

3 Higher Cortical Function AREAS Primary Sensory/Motor Areas touch, pain, vision, hearing DEFICITS loss of perception or movement Sensory/Motor Association Areas agnosia, apraxia, and Integrative Areas cognitive loss, loss of awareness (anosagnosia) Agnosia inability to use sensory information in complex ways although perception is preserved. Apraxia inability to perform complex movements without weakness or paralysis.

4 Somatosensory Lesions Agnosia With damage to sensory association areas while the primary sensory area is intact, patients can perceive simple aspects of a sensory stimulus, but complex aspects are impaired. A patient who can feel when they are touched, but CANNOT: identify an object placed in their hand identify a number drawn on their palm

5 Somatosensory Lesions Apraxia Damage to sensory or motor association areas produces an inability to perform familiar movements on demand in the absence of sensory or motor impairment. A patient who is not paralyzed, but CANNOT: walk with the normal stepping pattern show you the motion to brush their teeth demonstrate how to write their name

6 Higher Cortical Function In lesions that cause anosognosia, patients are typically unaware of their deficit. These lesions cause selective and restricted loss of self awareness for a specific modality, but maintain awareness for other modalities. In some cases this requires bilateral damage to same area in each hemisphere.

7 the where and what of objects Parietal Dorsal Path - where: analysis of object position and motion. Bilateral lesions: motion agnosia Temporal Ventral Path - what: analysis of form, color, faces, written words. Lesions: color/form agnosia, prosopagnosia, reading agnosia Visual System what where Large Occipital Lobe lesions: cortical blindness, Anton s syndrome. loss of awareness

8 Somatosensory System - Tactile Parietal lobe tactile recognition of objects attention to personal space integration of tactile/visual/language information; eye-hand coordination language visual Lesions: astereognosis, agraphesthesia, EDSS, apraxia, neglect

9 Somatosensory Lesions Model Patient Neglect inattention to contralateral side of the body and external world. Patient disregards visual, tactile, auditory stimuli from one side. Patient is unaware that anything is wrong. Lesion usually on right, but can also occur on left. May involve a visual deficit (left homonymous hemianopia) + unawareness.

10 Auditory System Auditory association cortex is involved in meaning of sound and understanding language. Comprehension (sensory): Temporal Lobe - Wernicke s area Speech (motor): Frontal Lobe - Broca s area Wernicke s Area word comprehension Word Memory: Temporal lobe Integrative areas: reading - visual/language braille - tactile/language Broca s Area speech

11 Lesions Affecting Language Aphasia is a disruption of language capability separate locations = differential effects Wernicke s Aphasia inability to understand meaning of words Fluent speech but nonsense meaning Unaware of deficit Broca s Aphasia understands words Nonfluent can t vocalize; word use affected Aware of deficit Superior longitudinal fasciculus connects Wernicke s and Broca s areas Lesions of integrative areas: affect visual and tactile aspects of language- reading, agraphesthesia

12 Language Shows Brain Asymmetry Surgery was performed on a group of patients with severe epilepsy in the 1960s. The cerebral hemispheres were disconnected by cutting the corpus callosum to prevent the spread of abnormal electrical activity from one hemisphere to the other. Studies (split brain experiments by R. Sperry/nobel prize and M. Gazzaniga) performed on these patients made the startling discovery that language was localized to the LEFT hemisphere in most of the patients.

13 Hemispheric Asymmetry Split brain experiments: hemispheres surgically isolated in patients with severe epilepsy stimuli (tactile, visual) presented to only one hemisphere without communication to other hemisphere what do patients report? what are innate capabilities of each hemisphere?

14 Split Brain Experiments Visual stimuli presented to: RT visual field - patient names object LT visual field - patient says nothing Patient draws object when pencil is placed in LT hand, but does not know why. Patient makes up an explanation for the drawing.

15 Split Brain Experiments Conclusions Speech resides in the LT hemisphere for most people (related to handedness). Information in the RT hemisphere must be transferred to Lt to speak about it and be consciously aware of it. The Lt hemisphere confabulates (fabricates an imaginary explanation) to compensate for lack of information. RT hemisphere controls the emotional content of language (intonation, singing). Can be used to retrain Broca aphasics by singing words when they cannot be spoken.

16 Language Shows Brain Asymmetry Language localized in Left hemisphere in most adults Related to handedness: RT handed - 96% have language in LT brain LT handed - 70%LT, 15%RT, 15%bilateral people - both languages in same hemisphere. Lesions may preserve one language but impair the other.

17 Unilateral brain lesions - tendency for clinical asymmetry: LT lesion RT lesion Space awareness neglect (parietal) Language speech aphasia (Broca) comprehension aphasia (Wernicke) emotional content singing Mood depressed (frontal lobe) cheerful (frontal lobe)

18 Frontal Lobe Motor Association Areas Planning and integration of movement Supplementary Motor Area Premotor Cortex Lesions cause apraxia.

19 PreFrontal Cortex Working memory and Personality How we store and manipulate information for short periods of time Dorsolateral area maintains working memory ; long-term planning and problem solving. Ventromedial area - personality awareness of social context of behavior emotional control. Lesions: cognitive deficits in reasoning, judgment, problem solving, control of emotions, disinhibition.