Brain Damage and Mental Function
Terms
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- Where are the lesions associated with alexia and agraphia?
- angular and supramarginal gyri (in parietal lobe)
- aphasia
- difficulties in the expressive use of speech
- agnosia
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- disorders of recognition and perception
- a loss of ability to recognize objects, persons, sounds, shapes or smells while the specific sense is not defective nor is there any significant memory loss
- It is usually associated with damage to the temporal lobe
- fail Mooney's face test and Unconventional views test - anosagnosia
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- the tendency to ignore or sometimes deny the fact that one has a problem/is paralyzed
- most often seen with right hemisphere damage
- patient may confabulate when asked to move paralyzed arm - right and left hemisphere associations
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right - associated with reality
left - associated with schematics and planning - Cases that indicate that certain areas of the brain are specialized
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- the woman whose right arm tried to strangle herself
- spontaneous smile vs. forced smile - Where does a natural/spontaneous smile originate from?
- basal ganglia (limbic system)
- natural gait vs. marching
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natural gait originates in basal ganglia
marching involves the motor cortex - too little dopamine vs. too much dopamine
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- Parkinson's disease
- too little dopamine = shuffling gait, parkinson's disease
- too much dopamine = chorea (excessive involuntary movements), schizophrenia - Most striking evidence of specialization
- lesion studies/evidence
- prosopagnosia
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- impairment in facial recognition
- damage in temporal lobe (usually right hemisphere) - Capgras Syndrome
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- patient thinks parents/loved ones are impostors
- disconnection between limbic system (amygdala) and visual system - Cotard's Syndrome
- Patient believes s/he is dead
- arcuate fasciculus
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- connects the posterior part of the temporoparietal junction with the frontal cortex in the brain.
- in left hemisphere
- connects Broca's area to Wernicke's area.
- Damage can cause conduction aphasia - conduction aphasia
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- damage to arcuate fasciculus (connects Broca's and Wernicke's areas)
- speech output sounds like Wernicke's patient
- syntactically normal but semantically abnormal
- comprehension intact
- difficulty in repeating words
- cannot read, alexic - Alexia
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- inability to read or name letters of the alphabet
- lesion in left visual cortex - Agraphia
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- inability to write
- lesion in left angular gyrus - How come an alexic can still recognize numbers and objects?
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-numbers: don't know. Maybe strong tactile connection with numbers and fingers
-objects: are polymodal, have many different attributes that they can be recognized by - somatosensory map - Penfield homunculus
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- located on postcentral gyrus of parietal lobe
- entire body is upside down, but head is right side up
- from top of head, down to side: genitals, foot, trunk, hand, thumb, face, lips, pharynx
- cortical magnificaiton: face and hand take up more space than other parts of the body - body image
- a brain's internal image and memory of one's body in space and time
- Medulla Oblongata
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-connects spinal cord to the brain
-controls critical functions like bp, hr, respiration
-connects to pons - Pons
- connects medulla to cerebellum
- Cerebellum
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- concerned with coordination of movements and timing
- coordinates muscular activity
- acheives motor control by receiving information from all around the body - cerebral cortex
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- outer part of each hemisphere
- where thinking and planning take place
- activation of entire cerebral cortex leads to arousal and wakefulness
- activation of a small portion leads to selective attention - thalamus
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- all sensory information except smell passes through it before reaching the outer cortical mantle
- evolutionarily more primitive
- main control center of sensation and movement
- all pathways travel to and from it
- damage can cause tremor, involuntary jerky movements, dystonia (uncontrolled movements), Parkinson's disease - hypothalamus
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- regulates metabolic functions, hormone production, and various basic drives such as aggression, dear, and sexuality
- influences eating, drinking, sleeping and waking, sexual behavior, organization for flight or fight and rage reactions, and response to reward and punishment - hippocampus
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- controls laying down of new memories
- in temporal lobe - Lateral Fissure
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- Sylvian Fissure
- separates frontal and temporal lobes - Central Fissure
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- Rolandic
- separates frontal and parietal lobes - relative localization
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- most functions can be assigned to a region of the cortex but without precise localization to specific cells
- the higher the function, the higher the degree of integration and the less localized the system - Neuroma
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- popular explaination for phantom limbs
- frayed and curled up nerve-endings at the site of the amputation become inflamed and irritates, fooling the brain into thinking the missing limb is still there - cell's receptive field
- each cell on the somatosensory cortex has its territoryy on the body surface to which it corresponds
- dorsal rhizotomy
- procedure in which all the nerve fibers carrying information from one arm into the spinal cord are completely severed
- one explaination for phantom limb pain
- as the brain adjusts to the loss of a limb and cells slowly make new connections, there is a slight error in the remapping so that some of the sensory input from touch receptors is accidently connected to the pain areas of the brain
- Patient was born without arms but she has phantoms that can move. What does this suggest?
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- the neural circuitry for her body image must have been laid down at least partly by genes
- body image is not strictly dependent on motor and tactile experience - What creates and maintains your body image in the brain?
- - parietal lobes combine information from sources such as muscles, joints, eyes, and motor command centers
- primary motor cortex
- concerned mainly with simple movements (like wiggling fingers)
- supplementary motor cortex
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- associated with more complex motor skills (like waving goodbye)
- passes specific instructions about the proper sequence of required movements to the motor cortex - When commands are sent from the supplementary motor cortex to the primary motor cortex, where else does the informationg go?
- - identical copies of the command signal are sent to the cerebellum and parietal lobes, informing them of the intended action.
- What are the cerebellum and parietal lobes important for?
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- help to compare your intention with your actual performance and modify the motor commands as needed
- parietal lobe contains your body image - What 2 sources does the phantom limb experience arise from?
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- remapping (via sprouting and activation of latent connections)
- each time time motor command center sends signals to the missing arm, info about the commands is also send to the parietal lobe containing our body image
- the convergence of info from these two sources results in a dynamic image of the phantom limb that is continuously being updated - Parietal Lobes
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- responsible for sensory convergence of vision, hearing and touch (also muscle and joint sense)
- creates an internal representation of the external world, including own body
- concerned with discerning the spatial layout of the external world
- allow you to navigate through space, reach out for objects and know where you are - hemianesthesia
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- primary sensory loss on one side of body
- damage to parietal lobe - hemineglect
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- damage to right parietal lobe
- complete indifference and neglect of left side of world
- left side of memories are neglected also
- if patient's attention is drawn to left side, will notice left side - parietal lobe damage can cause
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- inability to determine tactile quality
- loss of joint sense
- disordered spacial orientation (can't see mooney faces) - When you glance at any visual scene, what happens to what you see?
- - the message from the eyes is mapped onto the primary visual cortex. From there it is relayed onto the "how" and "what" pathways
- What is the "how" pathway?
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-info from the primary visual cortex is sent to the parietal lobes
- parietal lobes are concerned with discerning the spatial layout of the external world, allow you to navigate through space, reach out for objects and know where you are - What is the "what" pathway?
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- info from the primary visual cortex is sent to the temporal lobes
- temporal lobes are concerned with recognizing and naming individual objects and responding to it with the appropriate emotions - Temporal Lobes
- temporal lobes are concerned with recognizing and naming individual objects and responding to it with the appropriate emotions
- reticular activating system
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- tangle of neurons starting in the brain stem (reticular formation) that projects widely to vast regions of the brain
- All areas of the brain are interconnected in a + feedback loop that takes a stimulus from the outside world, extracts its salient features and the bounces it from region to region before eventually figuring out what it is and how to respond to it
- is believed to be the center of arousal and motivation - Frontal Lobes
- - concerned with abstract processes such as judgement, foresight, and planning
- Limbic System
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- concerned with emotional behavior
- evaluation of the emotional significance and potential value of events in the external world - Why does neglect only occur with right parietal damage?
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- the right hemisphere of the brain is specialized for emotions and holistic/global aspects of sensory processing. It has a broad "search light" that covers both the right and left side of the world
- the left hemisphere is specialized for language, and has a narrower search light that only covers the right side of the world.
- therefore, if left side gets damaged, the right side's search light can still notice things in both sides of the world, but not vice versa - mirror agnosia
- - when prompted to reach for an object that a patient sees in a mirror, the patient reaches into the mirror instead of in the area that the object actually is in space
- Explanations for mirror agnosia
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- the left side of the patient's world just doesn't exist so to them, the object must be inside the mirror
- difficulty with spatial task is because of parietal damage, not neccessarily due to the neglect itself. Patient can't do the proper mental gymnastics - Visual Agnosia
- - associated with lesions of the left occipital lobe and temporal lobes
- Why do normal people engage in psychological defense mechanisms?
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the left hemisphere takes in all the info given to it and organizes it into a stable belief system. But, if some new information comes along that doesn't fit into your belief system, you can't just rebuild your whole belief system, so you then resort to Freudian defenses: denial, repression, confabulation, and self-delusions
- allows coherence and stability within your own mind
- left hemisphere will do anything to maintain the status quo - Why are defense mechanisms so exaggerated in agnosognosia patients?
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- right hemisphere questions the status quo and looks for global inconsistencies. when anomalous info reaches a threshold, it forces a complete revision of the entire model/belief system
- doesn't matter what side the discrepancy comes from, the right hemisphere is always activated
- so if right side is damaged, the left hemisphere is free to pursue it's denial and confabulation as far as it wants - reaction formation
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- a subconscious attempt to disguise something that is threatening to your self-esteem.
- may explain anosognosia - astereognosis
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- loss of the ability to recognize objects by touch
- patient is unable by touch alone to name objects, describe them or demonstrate their use or significance - asymbolia / pain asymbolia
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- unable to recognize the nature of an object from the somatosensory information alone
- pain asymbolia - failure to correctly interpret pain sensations from areas of the body and are usually indifferent to pain - allesthesia
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- attention is paid to the spatial elements on the previously neglected side, but they are treated as if they were on the unaffected side
- associated with parietal damage - simultaneous extinction
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- the patient responds normally and attends effectively to both sides of space until there is simultaneous competing stimulation of both side. In that case, neglect of the side opposite of brain damage will occur.
- associated with parietal damage - apraxia
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- loss of intentional movements
- associated with parietal damage - cerebral commissurotomy
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- cutting the corpus callosum so that the two hemisphere can no longer exchange information
- patient referred to as split brain patient
- initially inteded to stop epileptic seizures from spreading from one hemisphere to the other - effects of commissurotomy
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- general lack of handicap
- since vision is contralateral, if something is shown in the left visual field, it is registered in the right occipital lobe: patient will know what is it but will not be able to verbally identify it since language is specialized on the left side, and the information cannot be transferred to the left hemisphere
- if object is placed in left visual field (seen by right hemi), can be picked up by left hand (controlled by right hemi), but not by right hand - synesthesia
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- A condition in which one type of stimulation evokes the sensation of another, as when the hearing of a sound produces the visualization of a color.
- associated with medial inferior of temporal lobe
- may be a crosswiring in color area and number area: in fusiform gyrus or angular gyrus - lower synesthete
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- cross-wiring in the fusiform gyrus
- V4 color area is near number area
- the color is driven by the visual appearance of the number, not numerical concept: roman numerals are not associated with color - higher synesthete
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- cross-wiring is in angular gyrus
- the color is driven by concept of sequence: any kind of sequence of numbers, days of the week, months of the year, have an associated color - subitising
- rapid, accurate, and confident judgments of number performed for small numbers of items just by looking at it
- semantics vs. syntax
- meaning vs. grammar
- Broca's aphasia
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- severely impaired speech output
- speech reduced to nouns and verbs
- meaning and word order intact
- difficulty with repetation and naming
- language comprehension intact. Can read - Wernicke's aphasia
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- characterized by a severe deficit in auditory comprehension
- related impairment in reading and writing
- difficulty with repetation and naming
- unintelligible, gibberish speech output - Wernicke's area
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- superior middle and posterior regions of the temporal lobe
- larger in left hemisphere than in right hemisphere - anomic aphasia
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- angular gyrus or supramarginal gyrus is damaged
- difficulty in finding words
- low vocabulary
- no comprehension of metaphors
- otherwise comprehension intact
- semantics and syntax intact
- damage to left A.G. - left/right condusion, dyscalculia
- cannot repeat - anomia
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- difficulty in finding the right words or the inability to remember names
- can repeat words - transcortical aphasias
- damage to the border zone surrounding classical language areas
- Stages of normal memory
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- perception
- contextual encoding
- short term memory buffer
- long term memory
- retrieval (recognition + free recall) - retrograde amnesia
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- failure to remember things that took place prior to what caused the amnesia
- things in the recent past are more likely to be lost and the older memories are more resistant to being lost - antirograde amnesia
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- a form of amnesia where new events are not transferred to long-term memory, so the sufferer will not be able to remember anything that occurs after the onset of this type of amnesia for more than a few moments.
- damage to the hippocampus, fornix, or mammillary bodies - Korsakoff's syndrome
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- antirograde amnesia caused by alcoholism (thiamine deficiency)
- can be caused by hypoxia (low blood pressure) or infections also
- intact short term memory
- confabulation (similar to right parietal damage)
- lack of awareness of passage of time
- anosognosia
- can acquire procedural and declarative memory, but won't remember actually acquiring it
- intact IQ
- mild euphoria - Parts of the Limbic System
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- Insular cortex
- Amygdala
- Septum: associated with pleasure
- Hypothalamic Nuclei
- Mammilary Bodies
- Fimbria and Fornix
- Nucleus Acumbens: associated with pleasure
- (Hippocampus)
- Anterior Cingulate
- Frontal Lobes - What part of the brain does the Rabies virus infect?
- Libmic System
- Input to the Limbic System
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- vision, touch, hearing, taste, smell
- sense of smell has dominant input because smell information goes straight from olfactory bulbs to limbic system - What applies brakes to limbic activity?
- anterior cingulate
- Output from Limbic System
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- Affective (subjective emotions)
- Behavioral (the four F's)
- Autonomic: sympathetic or parasympathetic
- Hormonal - Kluver-Bucy Syndrome
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- lesion in limbic system
- visual agnosia
- indiscriminate sexuality
- indiscriminate oral explorations - Hypothalamic Lesions
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- satiety center (nucleus): rats will keep eating
- appetite center: won't eat food but will drink water
- sexual nuclei
- pleasure center: give a high feeling
- septum: stimulation creates an orgasmic feeling - Temporal lobe epilepsy
- - characterized by complex sensory, motor, and psychic symptoms such as impaired consciousness with amnesia, emotional outbursts, automatic behavior, and abnormal acts
- Temporal lobe personality - interictal
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- personality changes, temporal lobe personality
- hypergraphia
- argumentative, stickyness in conversastion, egocentric, obsessive, hyper religiosity - Damage to frontal lobes
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- loss of higher attributes that define us as humans:
- morals, abition, empathy, etc.
- general change in personality - reticular activating cortex
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- in brain stem
- responsible for working memory
- allows you to hold information long enough to plan something
- attention - Frontal Lobe Syndrome
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- grasp reflex (undamaged FL's inhibit grasp reflex)
- loss of impulse control
impairment of:
- judgement
- perseveration
- morality
- planning
- ambition
- personality
- social norms
- sense of responsibility - motion blindness
- bilateral damage to middle temporal (MT) area
- color blindness
- bilateral damage to area called V4 (in fusiform gyrus)
- In visual system, what is the old and new?
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- Old path: from eyes to superior colliculus (to parietal and higher cortical areas)
- New path: from eyes, to lateral geniculate nucleus to primary visual cortex to where/how and what pathway to - "Where/how" pathway in visual system
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- from lateral geniculate nucleus to "where" pathway in parietal lobes
- associated with motion and position in space, visually guided motions - "What" pathway in visual system
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- from lateral geniculate nucleus to "what" pathway in temporal lobes
- associated with object identification, object's emotional significance, and color information - Blindsight
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- damage to primary visual cortex
- can't "see" but can still reach out and grab something in that area
- "new" pathway damaged, but "old," orienting pathway is still intact - Broca's area
- inferior posterior frontal cortex of left hemisphere
- Transcortical motor aphasia
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- lesions in frontal association cortex (anterior and superior to broca's area)
- doesn't understand speech
- cannot read
- can repeat without impairment - Transcortical sensory aphasia
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- lesion in peri-sylvian association cortex (junction of parietal and temporal lobes)
- language reception is severly affected but ability to repeat is intact - Septum
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- cluster of cells near the front of the thalamus in the middle of the brain (limbic system)
- activation of this areas creates intense pleasure - inner emotional life vs. outward expression of emotions
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inner: connections between amygdala and frontal lobes
outward: hypothalamus