midterm 2 Flashcards
what is functional segregation?
each level of sensorimotor hierarchy is composed of different units
sensory feedback
- sensory systems monitor body responses
- feed info back to sensorimotor circuits
- many adjustments that occur via SM feedback occur by unconscious mechanisms
- are carried out by lower levels of hierarchy (eg. spinal circuits)
ballistic responses
brief, all or none, high speed movements (sensory feedback is not involved)
main assertions of SM program theory
- LL of SMH possess sensorimotor programs that represent particular patterns of activity
- a particular complex movement is produced by activating combinations of these programs
- once particular level is activated, it can operate on basis of sensory feedback without direct control by higher level
motor equivalence
most movements can be carried out in a variety of ways (can produce same movement through different effectors)
EX: signing name with toes in the sand rather than using hand
what are the implications of having motor equivalence
indicates that SM program codes are independent of limb representation
the name signing motor program must be held at higher levels of SMH (?)
processes that influence learning of SM program (practice)
- response chunking = carrying out motor programs as chunks rather than individual units
- EX: typing “Vancouver” as a smooth set of movements
- shifting control to lower levels
- frees up HL for more esoteric aspects (eg. focus on the expression of musical performance rather than individual notes)
unconscious processes (circle illusion)
although people perceive the circles as different sizes, their SMS responds in an unconscious pattern as if they are the same
EX: they will open hand to same degree when asked to reach out for the circles
two major areas of SM association cortex
- posterior parietal association cortex
- dorsolateral prefrontal association cortex
function of posterior parietal association cortex
integrates info about current position of body parts with info about positions of external objects you wish to interact with
a mosaic of areas responsible for guiding movement
what is the somatosensory cortex
area of the parietal lobe
- controls eye movements
- implicated in attentional mechanisms (eg. visual selective attention)
Desmurget et al (2009)
- studied people who were undergoing neurological surgery for brain tumors
- when mild stimulation to various areas of posterior parietal association cortex, patient formed intention to perform particular actions
- greater intensity: felt like they had already performed those movements
lesions to posterior parietal association cortex
deficits in perception and memory of spatial relationships, accurate reaching and grasping, control of eye movement, attention
Apraxia (left side) and Contralateral Neglect (right side)
Apraxia
a disorder of voluntary movement that is not attributable to a simple motor deficit
- difficulty making specific movements (eg. artists would be able to paint on canvas but difficulties on an uncommon surface)
- damage is unilateral to LEFT posterior parietal lobe but symptoms are bilateral
- language production deficits are common
domains of action susceptible to apraxic errors
- imitation of gestures (especially meaningless ones)
- performance of meaningful gestures on command
- real or pantomime use of tools and objects
Goldenberg (2008)
showed there is actually only one domain that is reliably susceptible to apraxic errors => imitation of meaningless gestures
Contralateral neglect
due to large lesion to or dysfunctional activity in RIGHT posterior parietal lobe
- viewer-centered: unable to respond to stimuli to the left of their body (posterior parietal cortex)
- eyes tilted to the right
- actions are focused on the right (eg. not shaving left side of face)
- object-centered: unable to respond to left side of objects (superior temporal gyrus)
evidence that (contralateral) neglect is not complete
- when object is repeatedly presented at the same spot to the left, patients begin to orient to that spot even though they are otherwise unaware of
- patients are better at completing an incomplete drawing to their right if the complete version of the drawing is first presented to their left
function of dorsolateral prefrontal association cortex
involved in evaluation of external stimuli and initiation of voluntary reactions to those stimuli
- neurons in dorsolateral prefrontal cortex fire first
secondary motor cortex (input and output)
- receives input from association cortex
- sens output to primary motor cortex
- there are multiple secondary motor cortices
general function of secondary motor cortex
in general:
- involved in programming of specific patterns of movements
- takes instructions from dorsolateral prefrontal cortex
Electrical stimulation: elicits complex movements (often bilateral)
recordings: neurons become active just prior to initiation of a voluntary movement
involved in complex series of movements and mental rehearsal of those movements
mirror neurons
fire when individual performs a particular goal-directed movement or when they observe that movement performed by another individual
Rizzolatti (1990)
neurons in monkeys fired just as robustly when monkeys observed research move an object
neurons also fired when the placing was behind a screen (neurons fire NOT because of visual input but the understanding of what action is to be performed)
primary motor cortex conventional view
GENERAL : each site in PMC controls a muscle in the contralateral part of the body and each neuron produces movement of that body part in a particular direction
STIMULATION : (Penfield somatotopic layout of primary motor cortex)
- each area when activated produced contralateral muscle activation and a very simple movement
RECORDING : each neuron is movement direction-selective (ie. fires most rapidly to movements in one particular direction)
primary motor cortex (current view)
uses longer bursts of higher intensity current to match recorded motor responses
movements that resulted were not the muscle twitches or segregated joint rotations that Penfield observed
they were complex, involved coordination of many joints, and resembled meaningful actions
ie. there is no clear demarcation of where a certain part of the PMC is responsible for a certain pattern of actions — no clear demarcation of where one begins and the other ends
PMC (current view) : end point vs direction
If a particular PMC site is stimulated, the body part will reach the same end point regardless of its start position.
If monkeys performed natural body movements, firing of many primary motor cortex neurons was most closely related to END point of the subsequent movement not the direction
when stimulations were applied, elicited hand movements were roughly equivalent in frequency to what was observed during spontaneous activity
possible effects of damage to cerebellum
- loss of ability to precisely control direction, force, velocity, and amplitude of movements
- loss of ability to adapt patterns of motor output to changing conditions
- difficulties in maintaining steady postures (eg. standing)
- disturbances in balance, gait, and the control of eye movement
- impairments on measures of attention and executive control, procedural memory, working memory, language and visual-spatial processing
- impairments in the learning of new motor sequences.
what are reverse prism goggles used for
to check for damage to cerbellum
task: individual wears reversing prism goggles and throws darts
if there is damage to cerebellum:
- marked impairments in ability to adjust to goggles over time
- return immediately to baseline after taking off goggles (ie. shows no adaptation to prism goggles)
current views of cerebellar function
- plays fundamental role in timing. when damaged, motor commands and cognitive states are no longer appropriately selected and sequenced
- cerebellum is involved in sensorimotor imagery (it is active during imagined and real actions)
- it is a learning machine: supports the adaptive plasticity needed for the emergence of skilled behaviour
basal ganglia
group of complex interconnected nuclie that performs modulatory functions
are part of a neural loop that received cortial input from various cortical areas and transmits them back via thalamus to various areas of motor cortex
evolving views of basal ganglia function
traditional view: modulate motor output
current views:
- also involved in variety of cognitive functions
- promotes new skill learning
- acts as a tutor for the cortex to help consolidate new skills
initial symptoms of PD
(mild) slight stiffness and tremor of fingers, develops on one side and down legs, eventually becomes bilateral