Chapter 7 part 2 Flashcards
prefrontal cortex
- areas of the frontal lobe located anterior the motor functional areas (i.e., 4, 6, and 8)
- outputs to SMA and PMC
- active when planning behaviors
- active when new motor skills are being acquired
- includes areas that mediate higher mental functions
- language areas located here: Broca’s area (areas 44 and 45)
major divisions of the prefrontal cortex
dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), anterior prefrontal cortex (APFC) (frontal pole), medial prefrontal cortex (MPFC) (ventromedial prefrontal cortex)
medial prefrontal cortex (MPFC) or ventromedial prefrontal cortex
- important in decision-making
- houses orbitofrontal cortex
lesions on lateral side of prefrontal cortex leads to…
- varying degrees of working memory deficits (verbal or non-verbal)
- executive function deficits: poor inhibitory control, poor reasoning and problem solving; poor planning
- varying degrees of transcortical motor aphasia: similar to Broca’s, but different from it in that repetition is intact
other functions in frontal lobes
the tongue and taste system; olfactory system
taste pathway
- signal begins when a taste cell responds to a tastant
- 3 cranial nerves (7, 9, 10) carry signals to medulla via nuclear solitary tract (NST)
- from NST, some fibers go directly to thalamus and some go to limbic regions (e.g., amygdala)
- from thalamus signals go to insula and gustatory areas, which are also in frontal lobes
- from there, neurons reach also the orbitofrontal cortex
orbitofrontal cortex
thought to be involved in processing the reward value of food and the resulting motivation to eat food
five basic tastes
salt, sour, bitter, sweet, and umami
olfactory system
- transduction from odor to neural signal begins when the odorant attaches to a receptor in the olfactory epithelium
- signal is transmitted to olfactory bulb through tiny olfactory nerves that pass through holes of a bone (cribiform plate)
olfactory bulb relays signals to…
- primary olfactory cortex –> detect a change in external odor
- orbitofrontal cortex (secondary olfactory cortex) –> identifying smell
key functions in occipital lobe
primary visual cortex; “what” and “where” pathways
primary visual cortex
- area 17
- primary recognition of visual stimuli
- surrounding it in the occipital lobe is the association visual cortex
optic chiasm
- 50% cross: those from medial half of retina
- 50% do not cross: those from lateral half of retina
optic pathway
optic nerve –> optic chiasm –> optic tract –> synapse at lateral geniculate nucleus –> courses as optic radiations –> primary visual cortex
somatotopy of occipital lobe
- incoming fibers from lower retina stay inferior; form Meyer’s loop and travel in temporal lobe
- incoming fibers from upper retina stay superior; travel in parietal lobe
low retina
superior visual field
upper retina
inferior visual field
lesions in lower part of visual system (Meyer’s loop, temporal lobe white matter)
lead to upper visual field defects
lesions in the upper part of visual system (parietal lobe white matter)
lead to lower visual field defects
occipital lobe divided into…
- inferior visual field on top
- superior visual field on bottom
(divided by calcarine sulcus)
primary visual cortex lesions
- lesion in upper calcarine = lower field defect
- lesion in lower calcarine = upper field defect
testing visual fields
- perimetry: done with a computer; more precise, takes more time, more cost; looks for defects and charts their locations by having the patient stare at a light while other lights are flashed in the periphery
- confrontation method: done with fingers; less precise, quick and cheap
clinical signs of visual defects due to prechiasmal lesions
- if lesion is in retina –> visual field defects are usually: horizontal (left or right half of visual field), apex pints toward blind spot
- if lesion is in optic disc –> defecs are usually: vertical (superior or inferior half of visual field), constriction of visual field, enlarged blind spot
macular (central) vision sparing
- colateral from other arteries like middle cerebral artery
- spares the center of vision so that it is kept intact in both eyes
lesions in lateral side of occipital lobe beyond primary visual disturbances that are not associated with blindness
deficits in two streams of information: “what” and “where” pathways
areas of parietal lobe
primary sensory cortex and lateral left parietal lobe
Wilder Penfield
stimulated the sensory cortex in awake epilepsy patients and had report the sensations they felt:
- created a topographical map that represented the body surface on the primary sensory cortex (the homunculus)
- discovered that different body parts had disproportionate cortical representation (e.g., hands are very large)
- Penfield discovered 1 humonculus, but subsequent electrophysiological research revealed that there could be as many as 4 humonculi lined up next to each other representing sensations from muscle movement, pain and temperature receptors, discriminative touch, and proprioception
primary sensory cortex (S1)
- areas 3, 1, and 2
- somatotopic maps of contralateral body sensations
- receive projections from contralateral half of body
- proprioceptive information from muscles and joints arrive here, relaying info about the position of body parts in relation to one another
- links to motor regions in frontal lobes
lesions of primary sensory cortex (S1)
- varied degrees of focal impairment in sensation on the contralateral side of the body
- acute (immediate) stage
- chronic (later) stage
why do sensory modalities recove in the chronic (later) stage of lesions of primary sensory cortex (S1)
- secondary sensory cortex compensates
- thalamus compensates for sensation of pain and temperature
- all sensory cortices like vision and audition compensate for quality and intensity of pain
- insula and secondary somatosensory cortex allow for asymbolia for pain (sensation of pain without unpleasantness)
acute (immediate) stage of lesions of primary sensory cortex (S1)
loss of all sensory modalities on the contralateral side of body and/or face
chronic (later) stage of lesions of primary sensory cortex (S1)
- recovery of sensation of pain and temperature and crude touch sensation
- continued loss of fine aspects of tactile information on contralateral body (arm and face): loss of two-point discrimination, agraphesthesia (inability to recognize a letter outlined on the skin), astereognosis (inability to recognize form), loss of vibration and light touch
- continued loss of proprioception in contralateral body (arm and face); if leg is involved, see positive Romberg sign (ataxia when eyes are closed)
agraphesthesia
inability to recognize a letter outlined on the skin
astereognosis
inability to recognize form
lateral left parietal lobe (rostral inferior parietal lobule)
- involved in complex gesture and action responsibilities
- “mirror neurons”: imitation as a form of learning; emergence of spoken language from hand gestures
lesions of lateral left parietal lobe
apraxia –> patient loses the sense of what a particular movement is for (cannot recognize a gesture made by others or implement a movement when ordered)
Wernicke’s area
- mainly in temporal lobe
- surrounding sensory language areas (angular gyrus and supramarginal gyrus) in parietal lobe
- mostly in the left hemisphere because language is mostly lateralized to the left hemisphere
- connected to Broca’s area through the arcuate fasciculus (mostly in parietal lobe)
areas of parietal lobe
primary and association sensory cortex
association sensory cortex
superior and inferior parietal lobules
lesion in inferior parietal lobe
- at the angular gyrus: alexia (inability to read written language)
- at the supramarginal gyrus: conduction aphasia (understand what is said, but unable to repeat it)
alexia or dyslexia
inability to read written language
- alexia: acquired (e.g., stroke)
- dyslexia: developmental
conduction aphasia
understand what is said, but unable to repeat it
- damage to inferior parietal lobe at supramarginal gyrus
optic ataxia
inability to accurately point to or reach for objects under visual guidance in contralateral hand
- damage to superior parietal lobe; can occur in either hemisphere and affects contralateral side
alexia
damage to inferior parietal lobule at the angular gyrus
anosagnosia
- left visual field neglect
- a lack of awareness or denial of one’s own neurological deficit; in this case, the person might not realize they have a problem with their vision
- damage to areas involving the inferior parietal lobe
left visual field neglect
the person has difficulty paying attention to or processing information in the left side of their visual field
- often due to damage in the right hemisphere in the inferior parietal lobule
key functions of temporal lobe
- olfaction
- audition
- memory: medial temporal lobe
- areas overlapping with inferior occipital cortex: visual perception (“what” pathway)
olfaction
- olfactory nerve consists of multiple tiny nerve cells with axons that terminate in the olfactory bulb, which belongs to the central nervous system
- complex set of olfactory receptors on different olfactory neurons can distinguish a new odor from background environmental odors and determine the concentration of that odor
- axons from the olfactory sensory neurons converge in the olfactory bulb to form clusters called glomeruli
- inside each glomerulus, the axons contact the dendrites of mitral cells and several other types of cells
brain areas that mitral cells send signals to
- anterior olfactory nucleus
- piriform cortex
- medial amygdala
- entorhinal cortex
- olfactory tubercle
piriform cortex
area most closely associated with identifying the odor
medial amygdala
involved in social functions and associating an odor with an emotional reaction
entorhinal cortex
associated with memory
anosmia
loss of smell
- can be indicative of a serious neuropsychological problem (indicates there is a problem with one of the brain areas that the mitral cells signal to)
audition in the temporal lobe
primary auditory cortex; auditory association cortex
primary auditory cortex
- represent the acoustic frequencies and intensities of a large range of pitched and unpitched sounds (speech, music, environmental noises) so as to permit their recognition and spatial localization
- receives information from both ears (therefore, unilateral damage does not cause deafness)
auditory association cortex
- surrounding the primary auditory cortex in the posterior and superior parts of the temporal cortex
- concerned with the memory and classification of sounds (language comprehension)
auditory agnosia
pure word deafness (verbal auditory agnosia)
- cannot recognize speech sounds, but can recognize non-speech sounds and can produce normal speech
- unilateral lesions in dominant hemisphere
Wernicke’s aphasia
inability to comprehend language
- lesion in auditory association cortex, only in left hemisphere
non-verbal auditory agnosia-amusia
inability to recognize non-verbal sounds, including music and tone
- unilateral lesion in non-dominant hemisphere
amygdala
attaching emotional significance to events
- when damaged, there is a marked decrease in the ability to express emotions
memory in temporal lobe
cortical and subcortical structures of the limbic system
- entorhinal cortex
- hippocampal formation
- lesions: anterograde memory impairment (cannot form new memories)
commissurotomy
when hemispheres cannot communicate with each other
- cortical connections between homotopic points of the two hemispheres are severed
- each hemisphere therefore functions independently of the other and without access to the other’s sensations, thoughts, or actions
- put object in left hand (sensory information gets to right hemisphere); cannot name the object
- put the same object in the right hand, the patient can name it
Wada test
to see on which side is language before surgery
- inject sodium amobarbital into the carotid artery
- the sodium amobarbital anesthetizes the hemisphere on the side where it is injected, allowing the surgeon to determine whether that hemisphere is dominant for speech
