Higher Order Cerebral Function Flashcards
What are the 6 layers of the neocortex
- Dendrites and axons from other layers
- Cortical to cortical connections
- Cortical to cortical connections
- Receives inputs from thalamus
- Sends outputs to subcortical structures (other than thalamus)
- Sends outputs to thalamus
What is included in the primary cortex?
- Primary sensory cortex (somatosensory, visual, and auditory)
- Primary motor cortex
What is included in the association cortex?
- Unimodal association cortex: area adjacent to primary cortex involved in processing for a SINGLE sensory or motor modality (somatosensory, visual, auditory, premotor cortex, supplementary motor area)
- Heteromodal association cortex: integrating functions from MULTIPLE sensory and/or motor modalities (prefrontal cortex, parietal, and temporal heteromodal association cortex
What are Brodmann’s Areas?
- Cortex is divided based on microscopic appearance
- Correlates well with functional areas of the cortex
How is cortical sensory processing relayed?
- Sensory input travels to the primary sensory cortex via thalamic relay
- Primary cortices relay to unimodal and heteromodal association cortices
The primary somatosensory cortex (S1) receives input from where?
- Ventral posterior nucleus of the thalamus
- Ventral medial nucleus of the thalamus
What does the secondary somatosensory cortex (S2) respond to?
Responds to touch, pressure, limb position, and pain from both sides of the body
Describe the inputs as in pertains to parallel processing from Brodmann’s areas in the primary somatosensory cortex
- Muscle spindle afferents synapse in area 3a
- Cutaneous afferents synapse in areas 1 and 3b
- Joint receptors synapse in area 2
What symptoms may be seen with a lesion in the primary somatosensory cortex (S1)?
- Impaired 2 point discrimination
- Impaired localization of stimuli
- Impaired position sense
What does the unimodal association cortex do in terms of somatosensory perception?
- Found in brodmann’s area 5
- Receives input from the primary somatosensory cortex (S1)
- Integrates information between body segments and somatosensory modalities
- Process of stereognosis occurs here
What does the heteromodal association cortex do in terms of somatosensory perception?
- Found in brodmann’s area 7
- Receives input from brodmann’s area 5 and visual information
- Controls eye-limb processing for most visually triggers or visually guided movements
What does the primary visual cortex do?
- Found in brodmann’s area 17
- Receives input from the lateral geniculate nucleus of the thalamus
- Integrates information from both eyes about shape, color, size, location, and direction of movement for the contralateral half of the visual field
What is the difference in function between the dorsal and ventral pathways of the heteromodal visual association areas?
- Dorsal: analysis of motion and spatial relations (where are things around you?)
- Ventral: analysis of form and color (what are the things around you?)
Describe the primary auditory area (A1)
- In transverse temporal gyri
- Found in brodmann’s area 41
- Receives input from medial geniculate nucleus of the thalamus
- Responsible for sound frequency and location from both ears
Describe the secondary auditory area (A2)
- In transverse temporal gyri
- Found in brodmann’s area 42
- Receives input from medial geniculate nucleus of the thalamus
What does the auditory unimodal association area do?
- In transverse temporal gyri
- Found in brodmann’s area 22
- Interconnects with the medial geniculate nucleus of the thalamus
- Discriminates auditory frequencies , sequence, or pattern
- Projects to heteromodal association areas in prefrontal and parietotemporal areas
What is hemispheric specialization?
There is mostly symmetrical anatomy and functions of the left and right hemisphere, but some marked asymmetries functionally, which may eliminate communication delays between the hemispheres
Which hemisphere is typically dominant and why?
- Left hemisphere is typically dominant
- Controls simple movements for contrlateral limb and skilled tasks for both limbs (90% of people are right-hand dominant)
- Language center
What is lateralization and what makes it clinically relevant?
- Lateralization is the development of a “dominant” hemisphere that usually occurs before 3-4 years of age
- If damage occurs early in lateralization, language and handedness function can shift to the other hemisphere
- If damage occurs too late, function will not shift
What structures are involved in the core language circuit?
- Wernicke’s area
- Broca’s area
- Arcuate fasciculus
What is Wernicke’s area?
- Found in brodmann’s area 22
- Posterior 2/3 of superior temporal gyrus in the dominant hemisphere
- Adjacent to the primary auditory cortex
- Responsible for language processing to enable sequences of sounds and writing to be identified and comprehended as meaningful words
- Adjacent association cortex assist in language processing
What is Broca’s area?
- Found in brodmann’s areas 44 and 45
- Opercular and triangular portion of the inferior frontal gyrus
- Motor program to activate sequences of sound to produce words and sentences are formulated here and communicated to the face region of the primary motor cortex
- Adjacent areas assist with the production of speech
How do we repeat a word that we here?
Listen/read word > primary auditory of visual cortex > Wernicke’s area > sound is converted into a neural representation of the word > W communicates with B via arcuate fasciculus (subcortical white matter pathway) > Broca’s area > neural representation is converted back into sounds > primary motor cortex > corticobulbar tract
What are the symptoms of Broca’s aphasia?
- Decreased fluency
- Shorter phrase length
- Effortful and telegraphic speech that is monotonous and lacks grammatical structure
- Some preservation of over-learned tasks such as singing the happy birthday song
- Comprehension intact except for syntax
- Reading comprehension preserved
- Writing and reading aloud are both slow, effortful, and agrammatical
- Impaired repetition
What are the symptoms of Wernicke’s aphasia?
- Impaired comprehension
- Speech has normal fluency, prosody, and grammatical structure but lacks meaning
- Paraphasic errors
- Reading comprehension impaired
- Writing is fluent, but meaningless
- Unaware of deficit
- Impaired repetition
What is global aphasia?
- Lesion of both Broca’s and Wernicke’s area
- Not fluent
- Cannot comprehend
- Cannot repeat
What is mixed transcortical aphasia?
- Not fluent
- Cannot comprehend
- Can repeat
What is transcortical motor aphasia?
- Not fluent
- Can comprehend
- Can repeat
What is transcortical sensory aphasia ?
- Fluent
- Cannot comprehend
- Can repeat
What is conduction aphasia?
- Lesion between Broca’s and Wernicke’s areas, but the areas themselves are intact
- Fluent
- Can comprehend
- Cannot repeat
What is alexia?
Deficits in central language processing that impairss the ability to read, common in Wernicke’s aphasia
What is agraphia?
Deficits in central language processing that impairs the ability to write, common in Broca’s aphasia
What is apraxia?
- The inability to carry out an action in response to verbal command that is not directly caused by the absences of comprehension, motor function, or coordination
- Inability to formulate the correct motor sequence
- Not well localized and can be cause by a lesion in various locations
- 1/3 of patients with aphasia will also have apraxia
How is attention directed by the dominant and non-dominant hemisphere?
- The left hemisphere (dominant) mainly attends to the right side
- The right hemisphere (non-dominant) strongly attends to the left side and mildly attends to the right side
What attention impairment can occur with a lesion to the right hemisphere (non-dominant)?
Left hemisphere would continue to attend to the right side, but there will be profound deficit to attention to the left side
What attention impairment can occur with a lesion to the left hemisphere (dominant)?
The right hemisphere will attend to both the left and right sides, mild to no deficits will be seen due to compensation from the right hemisphere
What is the parietal association cortex?
- Located at the junction of the parietal, temporal, and occipital lobes
- Responsible for spatial analysis such as visual, proprioceptive, vestibular, auditory, and surrounding cortical inputs
- Information about surrounding environment and relative position of body in space
- Non-dominant hemisphere more active/important than dominant hemisphere
What is hemineglect syndrome?
- Profound neglect of the contralateral half of the external world and the person’s own body
- No awareness of deficit
- May fail to recognize that the left side of their body even belongs to them
- Occurs with lesions to right parietal cortex or right frontal cortex
What are the three types of neglect?
- Sensory neglect: patient ignores visual, tactile, or auditory stimuli from the contralateral hemispace (input is received, it is just ignored)
- Motor-intentional neglect: patient performs fewer movements in the contralateral hemispace
- Combination neglect (sensory and motor): both of the above deficits are present
- Conceptual neglect: patient’s internal representations of their own body or the external world exhibit contralateral neglect
What is important about the left and right hemispheres connections via the corpus callosum?
- Important in both recognition and production of the affective elements of speech
- Lesions in language areas on the non-dominant hemisphere can cause
- Receptive aprosody: difficulty judging meaning imparted by tone
- Expressive aprosody: difficulty producing emotionally appropriate expressions with voice
In general, what does the frontal lobe dictate?
Personaility
What can occur with lesions to the frontal lobe?
- Highly variable behavioral symptoms
- Behavior is contradictory and unpredictable
What are the three main cerebral arteries?
- Anterior cerebral artery
- Middle cerebral artery
- Posterior cerebral artery
(also contributing are the anterior and posterior communicating arteries for redundancy and to reduce effects of blockages)
What are some characteristics of MCA infarcts?
- Most common artery involved in infarcts of ischemic events
- Types: superior division infarct, inferior division infarct, deep territory infarct, proximal stem infarct
- Each type has its own deficits
- Deficits vary from left side to right side
Describe a left MCA superior division infarct
- Right face and arm weakness
- Broca’s aphasia
- Some R face and arm cortical sensory loss
Describe a right MCA superior division infact
- L face and arm weakness
- L hemineglect
- Some L face and arm cortical sensory loss
Describe a left MCA inferior division infarct
- Wernicke’s aphasia
- R visual field deficit
- R face and arm cortical sensory loss
- Mild right-sides weakness
Describe a right MCA inferior division infarct
- Profound L hemineglect
- L visual field deficit
- L face and arm cortical sensory loss
- Mild left-sided weakness
Describe a left MCA deep territory infarct
- R pure motor hemiparesis
- Larger lesions may produce cortical deficits such as aphasia
Describe a right MCA deep territory infarct
- L pure motor hemiparesis
- Larger lesions may produce cortical deficits such as L hemineglect
Describe a left MCA stem infarct
- R hemiplegia
- R hemianesthesia
- R homonymous hemianopia
- Global aphasia
- L gaze preference
Describe a right MCA stem infarct
- L hemiplegia
- L hemianesthesia
- L homonymous hemianopia
- Profound L hemineglect
- R gaze preference
Describe a left ACA infarct
- R leg weakness (hemiparesis with larger infarcts)
- R leg cortical sensory loss
- Frontal lobe behavior abnormalities
- Transcortical aphasia
Describe a right ACA infarct
- L leg weakness (hemiparesis with larger infarcts)
- L left cortical sensory loss
- Frontal lobe behavioral abnormalities
- L hemineglect
Describe a left PCA infarct
- R homonymous hemianopia
- Alexia without agraphia
- Aphasia, R hemisensory loss, R hemiparesis (thalamus and internal capsule)
Describe a right PCA infarct
- L homonymous hemianopia
- L hemisensory loss and L hemiparesis (thalamus and internal capsule)
