9. Perception and sensorimotor system Flashcards
What are the main structures for seeing in the eye?
Iris, pupil and lens
What are the visual receptors in the retina?
Cone receptors and Rod Receptors
What is the retina-geniculate-striate pathway?
Visual stimulus from the visual field is imputed through both the left and right eyes. Images from the right visual field travel through the nasal hermietinas in the right eye and the temporal hemiretina and vice versa for images from the left visual field.
Then the stimulus activates the Optic nerve and travels down the optic chiasm of each side. The Stimulus then ends up at the primary visual cortex of the opposite side. i.e. From the right visual
How many layers does the Lateral Geniculate Nuclei have?
Six layers.
What do layers 2, 3, and 5 of the LGN receive?
Receive input from the ipsilateral eye
What do layers 1, 4, and 6 of the LGN receive?
Receive input from the contralateral eye
What are the two systems of differential processing of visual stimuli?
Magnocellular system and Parvocellular system
What systems are involved in colour processing?
NO Magnocellular and YES parvocellular
What systems are involved in contrast sensitivity processing?
HIGH Magnocelular and LOW parvocellular
What systems are involved in spatial resolution processing?
LOW magnocelluar and HIGH parvocellular
What systems are involved in temporal resolution processing?
FAST magnocellular and SLOW Parvocellular
What layers of the LGN are involved in the Magnocellular system?
Layers 1 and 2
What layers of the LGM are involved in the Parvocellular system?
Layers 3-6
What is the laminar organisation of the primary visual context? i.e. What are the 6 layers of the neocortex?
- Axon and dendrites: few cell bodies
- Densely packed stellate cells: a few small pyramid cells
- Loosely packed stellate cells: intermediate sized pyramid cells.
- Brands of densely packed stellate cells; not pyramidal cells
- Very large pyramidal cells; a few loosely packed stellate cells
- Pyramidal cells of various sizes; loosely packed stellate cells.
What is white matter?
Myelinated pyramidal cell axons; few cell bodies
What are the main functions of the Primary visual cortex (V1)?
Receives information from the LGN.
Located in the posterior areas of the occipital lobe
Biggest portion is found in the Longitudinal fissure
What is the main function prestriate cortex and Inferotempral cortex (V2)?
Secondary visual context
Receives information from V1
Located around v1 in the occipital lobe, and in the inferotemporal cortex
What is the main function of the posterior parietal cortex?
Receivs information from V2 and from the secondary areas of other sensory systems.
Largest areas located in the posterior parietal cortex
What are the main areas of the cerebral cortex relevant to the visual system?
Posterior parietal cortex
Prestriate cortex
Primary visual (striate) cortex
Inferotempral cortex
What is the Dorsal stream?
From the V1 → dorsal prestriate cortex → Posterior Parietal Cortex
What is the ventral stream?
From the v1 → ventral prestriate cortex → Inferotempral Cortex
What are the two theories of the dorsal and ventral streams?
“where” vs “what” theory – What type of information
VS
“Control of Behaviour” vs “Conscious perception” Theory – How the information is used?
prosopagnosia
Also known as face blindness, is an inability to recognise faces.
What causes prosopagnosia?
Lesions often bilateral to occipito-temporal junctions (fusiform face area) of the fusiform gyrus.
What are the two distinctions of prosopagnosia?
Developmental prosopagnosia
Acquired prosopagnosia
Patients specifically have difficulties in recognising identities, but they can recognise the stimulus face per se.
Is prosopagnosia specific to faces? (can be, but not usually?)
What is explained by prosopagnosia?
Well explained by the “control of behaviour” vs. “conscious perception” hypothesis (damage at the ventral stream) → unconsciously recognised what consciously is NOT recognised
Greater physiological reactivity to familiar, significant faces than to unfamiliar faces
How are sensory systems organised?
Associated cortex -> secondary sensory cortex -> primary sensory cortex -> Thalamus (relay nuclei) -> Receptors
What is motor output guided by?
Sensory input
Except for ballistic movements
How does learning affect the sensorimotor system?
Learning (experience) changes the natural and locus of sensorimotor control. Conscious to automatic
What are the two divided areas of the sensorimotor association cortex?
Posterior parietal association cortex
Dorsolateral prefrontal association cortex
What does the posterior parietal association cortex determine?
It determines the location of body parts in space and relation to external objects.
Where does the posterior parietal association cortex receive input from?
Receives input from visual, auditory, and somatosensory systems
Where does output from the posterior parietal association cortex go to?
Output goes to areas of the frontal lobe.
- Dorsolateral prefrontal association cortex
- Secondary motor cortex
- Frontal eye field
Apraxia
Damage to the left posterior parietal lobe – it is the inability to execute voluntary (i.e. controlled) movement
Contralateral neglect / spatial neglect
Damage to right posterior parietal lobe – Problems in responding to stimuli contralateral to side of brain injury
What does the dorsal prefrontal association cortex initiate?
Initiates voluntary responses to stimuli
Where does the dorsal prefrontal association cortex receive projections from?
Receives projections from posterior parietal cortex
Where do projector outputs from the dorsolateral prefrontal association cortex go to?
Projections are sent out to the secondary motor cortex, primary motor cortex and frontal eye field
What is the secondary motor cortex involved in?
Involved in programming of specific patterns of movement
What is the secondary motor cortex composed of?
Premotor areas (dorsal and ventral)
Supplementary motor area (SMA, preSMA, supple. eye field)
Cingulate motor areas (x3)
Where does the secondary motor cortex receive inputs from?
Input mainly from association cortex
What do pre-motor areas and supplementary motor areas have connections with?
Primary motor cortex and each other
What is the supplementary motor cortex involved in?
SMA involved in internally generated motor sequences and implicit motor learning
What is the pre-motor area involved in?
Involved in externally guided motor sequences and explicit motor learning
What is the motor homunculus responsible for?
Responsible for execution of voluntary movement
What does the homunculus include?
Precentral gyrus of frontal lobe – motor strip
Mapped by Penfield and Boldry (1937)
Interplay between corticol sites and sensory systems
What does damage to the primary motor cortex cause difficulty to?
Difficulty moving one part of body independently of another
Reduces speed, force, and accuracy of movements
But voluntary movement can still occur
Astereognosis
Astereognosis
Problems identifying objects via touch (stereognosis)
What are the subcortical sensori motor structures?
Cerebellym and Basal Ganglia
What do the subcortical sensorimotor structures do?
Interact with different levels of the sensorimotor hierarchy
Coordinate and modulate sensorimotor activity
What does cerebellum play a rule in?
Plays a role in feedback of motor movements and has neural programs for skilled movement
Where does the cerebellum receive information from?
Primary and secondary motor cortex
Muscle and joint receptors and vestibular, somatosensory, visual, and auditory systems (feedback)
Brain stem nuclei (re. descending motor signals)
What is the basal ganglia a collection of?
Collection of connected yet independent cerebral nuclei: the caudate and putamen (straitm), globus pallidus, amygdala
What does the basal ganglia do?
Planning and producing movement
What does the basal ganglia contribute to?
It does not contribute to descending motor pathways but receive cortical input and transmit via thalamus to motor cortex
How do neural signals get conducted from the primary motor cortex to the motor signals of the spinal chord?
Over four pathways
- Dorsolateral corticospinal tract
- Dosolateral corticorubrospinal tract
- Ventromedial corticospinal tract
- ventromedial cortico-brainstem-spinal tract
Which systems are involved in the dorsolateral pathways (pyramid system)?
Dorsolateral corticospinal tract
Dorsolateral corticorubrospinal tract
What can damage to the dorsolateral pathways cause?
Inability to control individual joints and limbs
What systems are involved in the ventromedial pathways (extra-pyramidal system)
Ventromedial cortico tract
Ventromedial cortico-brainstem-spinal tract
What does the ventromedial pathway control?
Controls posture, whole-body movements (e.g. walking and climbing, and influences spinal reflexes
What are central sensorimotor programs?
Patterns of programmed activity Motor equivalence May not be conscious Practice - innate behaviours that occur without practice - response chunking - hierarchial controls
