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Midterm

PSYC 251 Study Guide - Midterm Guide: Premotor Cortex, Motor Planning, Motor GoalPremium

14 pages481 viewsFall 2016

Department
Psychology
Course Code
PSYC 251
Professor
Adam Krawitz
Study Guide
Midterm

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Psychology 251 - Exam 2
Topic 3: Perception - Bottom-up and Top-down influences
- Bottom-up - stimulus driven, feedforward connections. Depends on the proximal stimulus and
genetic “hard-wiring” of sensory systems
Involves low-level-processing intermediate high-level processing
to determine what something is based on information given form the
stimulus
- Top-down - Driven by goals and expectations, feedback connections.
Depends on past experience, internal state, and environmental context.
We perceive the world in a way that is “most likely’ based on our past
experiences
- Perception depends on both types of processing!
- Interactive activation theory: McClelland and Rumelhart - model of
letter and word perception; integrates bottom-up and top-down processes.
Knowledge of a word helps interpret what letters are in it (rather than the
other way around).
Features letters words = bottom-up processing uses feature
detectors; features excite or inhibit letters, letters compete with other
letters and excite or inhibit words.
Words letters features = tyop-down processing; words compete
with other words and excite letters.
Word superiority effect - bottom-up and top-down processes are necessary to explain
perception.
Topic 4: Action
Action is a change in the environment.
- Somatic - skeletal muscle - moves limbs
- Autonomic - controlled by the brain. Includes smooth muscles (blood pressure, digestion), cardiac
muscles (heartbeat), endocrine glands (secrete hormones), and exocrine glands (sweat, saliva).
- Internal actions - CNS: can the brain/mind take actions on itself?
Update memory, switch tasks, etc. Very similar to brain functions used to take physical actions.
PROBLEM: How do we effect change in the world?
IMPORTANCE: Actions are necessary to achieve goals (eating, drinking, reproducing, etc)
CHALLENGE: Inverse problem - determining what actions to take in order to achieve goals. (we work
backwards to figure out what we need to do to get there).
Motor System
- Motor control is hierarchical
- Motor equivalence - our movements are consistent with
abstract motor plans (motor plan is not represented as a
movement of specific muscles, but rather the general
movement in space)
Our writing appears similar (apart from quality) with
each body part used to write (hand, foot, teeth, etc.)
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- Inverse model - current position and desired
position - what sequence of motor commands is
needed to reach a desired position?
Used to create motor plans
- Forward model - current position and motor
commands predict the position that will be ended
in.
Used to evaluate motor plans and/or action
Efferent copy - internal copy of a motor
command. Compare actual behaviour and
predicted behaviour to make sure/know if
actual outcome matched predicted behaviour.
- Feedforward control - motor command to muscle;
fast but less accurate (inverse)
- Feedback control - motor command sent to muscle;
actual outcome compared to the desired state.
Adjustments made based on errors (forward)
Motor planning - PREMOTOR CORTEX
- Planning of voluntary actions begins at a conceptual
level based on goals
Quench thirst (goal) drink from cup (conceptual)
pick up cup (effector) activate muscles in arm
(implementation)
- Premotor cortex is involved in selecting goals and
planning actions at a conceptual level, particularly
when plans are driven by external stimuli.
Readiness potential - planning in the premotor cortex occurs before voluntary movement.
Precedes action sometimes ~1 sec before.
Planning for multiple alternative actions:
o Task: Reach for target with arm
o Spatial cues: cued with two possible targets (red and blue); different action for each target
o Memory period: cues are removed, prepare for both actions
o Colour cue: cued with actual target, now prepares for single action
o Go signal: initiate action. (most activity for the chosen action
plan at this point.)
- Mirror neurons - some neurons in the premotor cortex represent
actions at a conceptual level.
Performing or observing an action, ex breaking a peanut.
Whether breaking a peanut or watching someone else do it, the
neuron fires. Hearing not seeing/seeing not hearing - still fires
(So not a visual, perceptual, or auditory neuron).
Consistent with the idea that these neurons represent action
concepts, not the specific muscle movement.
Motor sequencing - SUPPLEMENTARY CORTEX
- This is adjacent to the premotor cortex. Involved in selecting goals and planning actions at a
conceptual level.
- Involved in selecting goals and planning actions at a conceptual level, particularly when plans involve
internally generated sequences of actions (like tying shoelaces, playing a song, performing a dance).
- Recording from SMA neurons during different movement sequences; using peristimulus time
histogram - each little mark when a neuron fires (action potential); each row is a trial. Pick event (one
action in a sequence) to line data up on.
One neuron fires in anticipation of a particular sequence.
One neuron fires before a particular action in a particular sequence
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One neuron fires before the third action in every sequence
- Behavioural performance with SMA deactivated by muscimol injection
(GABA agonist)
Injection of muscimal temporarily lesions supplementary motor
areas - could perform cued sequence just fine, but could not
perform learn sequence with the SMA (Supplementary motor area)
deactivated.
Circle = cue for specific action
Square = cue for learned action
Triangle = action
Blue = correct, red = error
Motor representation - MOTOR
CORTEX/SUPERIOR COLLICULUS
- Motor cortex represesnts directional
movements of body parts, not specific
actions.
- Signals from the motor cortex traced directly to lower motor neurons and
lower circuit neurons in the brainstem and spinal cord.
- spinal cord (lower motor neuron) medulla (pyramidal decussation)
pons midbrain (upper motor neuron) primary motor cortex
(precentral gyrus)
- Topography and cortical magnification are the same for the motor cortex
as in the somatosensory cortex (both side by side strips on the brain - one
receives input, one controls movement output)
- Motor homunculus - more cortex to hand control than in the somatosensory homunculus, less arm
and leg motor control.
- Motor cortex activity is correlated with movement
direction
Task: move joystick from center to a peripheral
target. Recordings from a single motor cortex
neuron show firing increases with direction of
movement; most firing in the preferred direction of
movement. Ex: if neuron prefers downward
movement, it fires the most when joystick is moved
from center to down.
Response rate as a function of directino of
movement can be summarized by a tuning curve;
tuning curves can be used to create a population
vector
Each vector represents the direction of movement
that a neuron prefers; length = how much that
neuron fires. Add to get the vector between the two which is the predicted direction of movement =
population vector. This accurately represents actual movement direction.
So direction of the population vector will predict the
direction of a forthcoming movement.
Motor targets - INTRAPARIETAL CORTEX
- Intraparietal sulcus (IP) helps to guide movements to
the correct location, orientation, and configuration.
Lateral (LIP) represents space for eye movements -
retinal-centered receptive fields. Location is relative to
where the eyes are looking.
Ventral (VIP) represents space for facial movements 0
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