Functional Localisation Flashcards
What are the anatomical orientations?
Dorsal/superior, Ventral/inferior, rostral/anterior, caudal/posterior, lateral and medial
What does ipsilateral mean?
Two structures on the same side. Ipsilesional refers to impairments on the same side as the damage
What does contralateral mean?
Structures on both sides. Contralesional refers to impairments on the opposite side of the damage
What are the planes of section?
Sagittal plane (side view, cut rough the middle/front of the brain), coronal/frontal plane (front view, cut through middle horizontal), transverse/horizonal plane (view from above. The lateral view depicts the surface of the brain
What are the largest part of the brain
Cerebrum is the largest (divided into two hemispheres) and the cerebellum is the smaller part which is primarily involved in co-ordinating movements
How many ventricles are in the brain?
The brain contains four ventricles which contain cerebrospinal fluid
What is white and grey matter?
Neurons form white matter (axons) and grey matter (cell bodies). Grey matter is on the outside (cortex) with the white matter underneath. The corpus callosum which connects the two cerebral hemispheres is a bundle of white matter. There are additional grey matter subcortical structures
What are characteristics of the cortex?
It is folded and 3.4mm thick. If unfolded it would stretch to 0.23 square metres. It hasgyri, sulci and fissures
What are Gyri?
The ridges. These include the inferior temporal gyrus, superior temporal gyrus, inferior frontal gyrus and postcentral gyrus
What are sulci?
The grooves. These include the precentral sulcus, central sulcus (which separates frontal and parietal lobes), postcentral sulcus, and parieto-occipital sulcus
What are fissures?
A deep sulcus. These include the lateral fissure (which separates the frontal and temporal lobes) and the longitudinal fissure
What are the four cerebral lobes that are in each hemisphere?
Frontal, parietal, temporal and occipital lobe. Each are associated with specific functions, some being the same on both sides and others being different
What is an example of a lateralised function?
Language which is usually lateralised to the left side of the brain
What is the function of the brainstem?
It controls the basic ‘primitive’ functions. Brainstem damage can cause lethargy or coma…or death
What are the parts of the brainstem?
The midbrain, pons and medulla
What are the components of the visual system?
Temporal retina, nasal retina, optic nerve, optic chiasm (where 1/2 information from each eye crosses over to be processed on opposite side), optic tract, LGN, optic radiations (superior visual field in inferior optic radiations and inferior in superior) and V1
Where are the optic radiations located?
Inferior located in the temporal lobe (process upper parts of visual field) and the superior located in the parietal lobe (process lower visual field)
How is the visual field represented?
It is topographically represented in contralateral V1, with inferior portions of the visual field located superiorly, and foveal regions at the occipital pole. Increasingly peripheral regions are represented towards middle of the brain
What is the visual field?
Everything that can be seen whilst fixating. Any area of blindness is a visual field defect
What happens as a result to damage to the primary visual structures?
Characteristic patterns of visual loss. Eg damage to v1 in one hemisphere will lead to hemianopia in the contralesional visual field
What are types of visual field defect?
Quadrantanopia (1/4 loss of vision), hemianopia (1/2 loss of vision), scotoma (less clearly defined area of loss)
What is the difference between pre-chiasmatic, chiasmatic and post-chiasmatic lesions?
Pre: generally cope fairly well in everyday life eg loss of vision in one eye. Chiasmatic: eg bilateral hemianopia, so lose vision of areas that cross over (peripheral vision). Post: significantly greater impairments in everyday life, such as homonymous hemi/quadrantanopia
Where does higher order visual processing occur?
In the visual association cortex. Unilateral lesions to these areas are more common which means impairments in these functions can be more subtle or lateralised than with bilateral lesions
Where is colour processed?
By the V4 complex, which is in the ventromedial occipitotemporal cortex
What is a disorder of colour perception?
Cerebral achromatopsia. No colour, but still have activity and luminance. Intact V1 but damage to ventromedial occipitotemporal cortex. Bilateral damage leads to full-field cerebral achromatopsia but this is rare. More common is V4 damage in one hemisphere resulting in contralesional achromatopsia
Where is visual motion processed?
By V5/MT (middle temporal gyrus). Motion perception deficits have also been associated with the cerebellum (involved in perceptual stabilsation)
What is a disorder of motion perception?
Cerebral akinetopsia. Inability to perceive visual motion. Intact V1 but large bilateral lesions to posterior portions of V5/MT. Severe akinetopsia results from bilateral lesions but this is very rare. More common is unilateral lesions which lead to less intense impairments
What are object perception impairments associated with?
The lateral occipital complex and left fusiform gyrus
What is neglect?
A syndrome characterised by impairments in visuospatial attention. An abnormality in the ability to orient attention to, or respond to the contralesional side of space which is not attributable to a primary sensory or motor deficit
Where does neglect usually occur?
Usually the left side of space which is impaired following right hemisphere damage. Has also been observed following damage to a variety of structures including right parietal and prefrontal cortices, and subcortical areas, but is classically and primarily associated with the right posterior parietal cortex
What is the motor homunculi?
Face and hand areas on the lateral surface (more neurons for these areas). Feet and legs in interhemispheric fissure. Contralateral upper limbs represented on lateral surface and low limbs on medial surface
What brain areas controls movement?
Motor cortex (precentral gyrus; part of the frontal lobe)
What area is involved in tactile processing?
Somatosensory cortex (postcentral gyrus; part of the parietal lobe). Contralateral upper limbs represented on lateral surface and low limbs on medial surface
What additional areas are involved in producing meaningful actions and action sequences?
Cortical areas such as the parietal cortex and premotor regions of the frontal lobe, especially those in the dominant (usually left) hemisphere
What is praxis?
An action based on will (intentional, not reflexive)/skilled movement ability
What is a disorder of praxis?
Apraxia, resulting from lesions to the praxis network. Loss of ability to perform learned skilled movements (physically could though. Loss of ability to plan and perform the sequence of actions). It is a disorder defined by exclusion, and a disorder of skilled movement not caused by an impairment of motor skills, sensory loss, perceptual deficit, a comprehension deficit or loss of motivation
How do individuals with apraxia present?
Cannot carry out actions to command but may perform the action spontaneously. Impaired production of symbolic gestures. Impaired imitation of symbolic and nonsense gestures. Greatest difficulty in pretend use of objects
Which areas typically result in apraxia if lesioned?
More common after left hemisphere lesions, generally left hemisphere lesions of the parietal and premotor areas
What areas are also involved in aspects such as coordination and timing of movements?
The cerebellum (movement coordination, balance, posture, motor learning, timing of movement, fluidity of movement) and basal ganglia (sequence of coordinated movement - procedural)
What is langauge?
Systematic use of sound combinations for communication purposes, that is guided by rules (different to speech). It is a spontaneously acquired form of symbolic communication
What are symbols?
Transmitted via gestures and vocalisations
What is speech?
An articulatory manifestation of language
What are examples of language disorders acquired after brain damagae?
Dyslexia/alexia (disordered reading), dysgraphia/agraphia (impaired writing), aphasia (disturbance in comprehension and production of speech, commonly due to stroke, but not due to sensory disorder, perceptual problem, thought disorder or disorder of movement)
What does language depend on?
An extended neural network, and language disorders occur after damage to this network (damage to the left cerebral hemisphere - localisation of function)
What is Broca’s aphasia?
Expressive/motor/non-fluent aphasia. Speech and language comprehension is intact but speech production is impaired
What is a case study of Broca’s aphasia?
Tan (epilepsy so question of generalisability/case study problems) at age 30 developed a right hemiparesis/loss of speech. Comprehension remained intact but unable to produce meaningful speech and died a few days later. Found a large cavity in left inferior frontal lobe and the site of injury was pronounced as the ‘special faculty of articulated language’
How does Broca’s aphasia usually present?
Speech that is non-fluent, effortful, dysarthric, dysprosodic, agrammatic (varying severities). Agrammatism (word order impaired), verbal economy (content words for intended meaning favoured compared to grammatical words) and omission to define articles and function words such as prepositions. Understanding can be impaired by syntactic ambiguities
What are additional problems that can be seen in patients with Broca’s aphasia?
Speech repetition, naming (some anomia), reading/writing problems (in same way as speech)
What is Broca’s area?
Left inferior frontal gyrus. Brodmann’s areas 44/45. If the damage is only to Brocas area, then aphasia usually results in only transient deficits. Broca’s aphasia usually only persists with additional damage to underlying white matter and basal ganglia
What was the historical view of Broca’s aphasia?
Loss of motor forms of speech, but this fails to explain agrammaticism and impaired syntax
What is Wernicke’s aphasia?
Receptive/sensory/fluent aphasia. Speech production is intact but speech comprehension is impaired and the primary deficit. Impaired comprehension of all speech, including own (unable to monitor self for coherent speech and cannot correct mistakes/errors), so in practice, speech comprehension and production are affected
How does Wernicke’s aphasia present?
Speech is typically fluent, well articulated, syntactically and prosodically correct, loghorrea, preservation of social conventions, presence of neologisms (creation of new words) and paraphasias (unintended syllable replacement)
What are additional problems seen in some patients with Wernicke’s aphasia?
Speech repetition, naming (some anomia) and reading/writing
What is Wernicke’s area?
Left posterior superior temporal gyrus. Correlation between severity of comprehension loss and amount of lesion in Wernicke’s area, but not overall temporoparietal lesion size
What is evidence of right hemisphere language?
Left hemisphere is specialised for phonological and syntactic processing, but 95% patients with right hemisphere damage admitted to rehabilitation units have communication problems. May be either hyporesponsive or hyperresponsive (need to contact relatives to determine how different these are to usual functioning for the patient). Also non-literal language is taken literally
What is right hemisphere language deficits referred to?
Crossed aphasia. Occurs where the lateralisation of language is revered and the right hemisphere is language dominant. As it is typically involved in aspects of speech such as interpreting non-literal language, pragmatics and prosody, this is where the deficits are seen
What are pragmatics?
The relationship between language and social contexts, including purpose of communication. Crossed aphasia patients take fewer turns and talk more about themselves, as well as having a tendency to prolong conversations rather than taking cues from the conversational partner to end
What is prosody?
The rhythm, stress and tonal modulation of speech. Crossed aphasia patients may have problems with both production and comprehension of speech (aprosodia)
What is retrograde amnesia?
Impairments in memory for events that happened prior to the brain damage, but not very old memories, eg of 5 years before incident
What is anterograde amnesia?
Impairments in memory for events that occur after the brain damage (Dory)
What is global amnesia?
Deficits relating to both retrograde and anterograde amnesia. In most patients, both impairments happen to some extent together, with one more pronounced)
What areas are associated with long-term declarative memory?
Medial temporal lobe and associated subcortical structures eg hippocampus (HM 16 year retro/anterograde amnesia), medial thalamus, mamillary bodies (Korsakhoff’s syndrome)
What causes dysexecutive syndrome?
Damage to the frontal lobe
What is dysexecutive syndrome?
Characterised by impaired inhibition (impulsivity), planning and working memory, mood disturbances (emotional lability), perseverative thoughts and actions and the re-emergence of primitive reflexes
What areas are often involved in a frontal lobe syndrome?
Prefrontal cortex, dorsolateral prefrontal cortex, orbitofrontal prefrontal cortex, ventromedial prefrontal cortex
