Action part 1 Flashcards
What is action?
Action is a physical movement triggered by the brain in response to stimuli or thought, involving muscle contractions. It can be voluntary (e.g., moving a hand) or involuntary (e.g., reflexes).
nothing here
Overview of motor system( S, A, M, CNS
Somatic Nervous System: Controls voluntary muscle movements.
Autonomic Nervous System: Manages involuntary functions like heart rate and digestion.
Motor Pathways: Carry signals from the brain to muscles for movement.
CNS Integration: Processes sensory input and plans movements.
Levels of Movement Control( Higher, Mid, Lower)
Higher centers (Cortex): Plan and initiate voluntary movements.
Mid-level (Brainstem, Spinal cord): Coordinate and refine movements.
Lower levels (Muscles): Execute the movement.
Motor Equivalence
The same motor plan can be executed by different effectors.
Motor plans are stored abstractly and translated into specific muscle commands.
Inverse model
Inverse Model
Current position & desired position → motor commands.
Used to create motor plans (how to move to reach the goal).
Forward models
Forward Models
Current position & motor commands → predicted future position.
Used to check if the movement plan will succeed.
Nothing here
Feedforward Control and Feedback Control
Feedforward Control: Motor command sent directly to muscles for fast execution, less accuracy. Used by inverse models to quickly generate motor plans.
Feedback Control: Motor command sent to muscles with real-time adjustments based on errors. Slower but more accurate, used by forward models to correct movements.
Levels of Action Planning
Goal: Quench Thirst
Conceptual Level: Decide to drink from a cup.
Effector Level: Pick up the cup with the right hand.
Implementation Level: Activate arm muscles.
readiness potential
Readiness potential: premotor cortex starts preparing for movement well in advance.
Arm Reaching Task and Premotor Neurons
Task: Reach for Target
Spatial Cues: Monkey sees two targets (red & blue).
Memory Period: Cues removed, monkey prepares both actions.
Color Cue: Monkey is cued with the actual target and prepares a single action.
Go Signal: Monkey initiates the action.
Mirror neurons in premotor cortex
Some neurons in premotor cortex
represent actions at a conceptual level
- Mirror neurons active when performing or
observing an action
Example of premotor cortex
Example: breaking a peanut
a. Breaking a peanut
b. Watching and hearing someone else break a peanut
c. Watching someone else break a
peanut
d. Hearing someone else break a peanut
Supplementary Motor Cortex (SMA)
Involved in goal selection and action planning at a conceptual level.
Especially for internally generated action sequences:
Tying shoelaces
Playing a song on a piano
Performing a dance sequence
SMA and Action Sequences
Animals trained to perform sequences like:
Sequence 1: push, pull, turn
Sequence 2: pull, turn, push
Individual SMA neurons show strong activity before specific sequences, with different neurons tuned to different actions.
The SMA plans both the actions and their order.
Nothing here
Primary Motor Cortex
Represents directional movements, not specific muscle actions.
Sends signals directly to lower motor neurons and circuit neurons in the brainstem and spinal cord
Topography and cortical magnification
Each hemisphere of cortex controls the contralateral side of the body.
Homunculi
Directional
selectivity in
M1(Primary Motor Cortex) neurons
Motor cortex activity correlates with movement direction.
Neurons are directionally tuned – higher firing rates for movements in preferred directions.
nothing here
Tuning curve for directional selectivity
Response rate as a function of direction of movement can be
summarized by a tuning curve.
Recordings and tuning curve for a single motor cortex neuron.
From tuning curves to a population vector.
Movement at 110°
Population vector: the sum of the
vectors for all active neurons
Nothing here
nOTHING HERE
Population vector in M1
Population Vectors in M1
Neuron firing = vector (direction = preferred, length = firing rate).
Sum vectors to create a population vector.
Represents movement direction and motor plans in M1.
Motor initiation &
basal ganglia
Motor initiation is the process of starting a movement. The basal ganglia are brain structures that help regulate and control voluntary movements, ensuring smooth execution.
Basal Ganglia
Basal Ganglia
Three components: Subthalamic nucleus, substantia nigra.
Help select, initiate, and inhibit movements via two loops:
Indirect pathway
Direct pathway
Cortico-Basal Ganglia Loops
Direct Pathway:
Cortex → Striatum → GPi + Substantia Nigra → Thalamus → Cortex
Excitatory – initiates action.
Indirect Pathway:
Cortex → Striatum → GPe → Subthalamic Nucleus → GPi + Substantia Nigra → Thalamus → Cortex
Inhibitory – inhibits action.
Basal Ganglia(SNc)
Pathway Activation
Substantia Nigra Pars Compacta (SNc):
Releases dopamine.
D1 Receptors (direct pathway): Excited by dopamine → Reinforces action.
D2 Receptors (indirect pathway): Inhibited by dopamine → Suppresses competing actions.
Dopamine bursts from rewards strengthen the direct pathway and weaken the indirect pathway, enabling reinforcement learning and behavior modification.
Huntington’s Disease
Parkinson’s Disease
Huntington’s Disease
Caudate nucleus atrophies.
Impaired indirect pathway → chorea (involuntary movements).
Parkinson’s Disease
Destruction of dopaminergic neurons in the substantia nigra.
Direct pathway inhibited, indirect pathway more active.
Symptoms: Slow movements, difficulty initiating movement
Basal Ganglia Processing
Cortex sends input (movement, cognition, emotion).
Striatum (caudate & putamen) receives signals.
Globus Pallidus & Substantia Nigra process and modulate activity.
Thalamus relays signals back to cortex to execute responses.
