Modulation Of Movement By The Basal Ganglia

Question 1

Freeze et al (2013)

Answer 1

Optogenetics
Excited Garvey at D1 expressing pathway
Showed stimaluating ON pathway gets activation but OFF pathway makes animal stop moving
Evidence BG is able to then on and off actions = indicates function of the BG

Question 2

What did Redgrave et al (1999) hypothesise?

Answer 2

The BG js the central switch in the brain which enables action selection for a particular situation

Question 3

Action selection

Answer 3

There’s predisposing conditions (sensory input, cognitive state, homeostasis etc) that all contribute to whether an action will be selected or not
Not all potential actions can be expressed at a time so have to select the action that will gain access to limited motor resources and translates to an action

Question 4

Idea of BG as a central switch - summary

Answer 4

It receives widespread input.
Tonic inhibition and selective release appear to be a mechanism for gating motor programmes.
Functional loops and topography support the idea of action ‘channels’.
Spiny projection neurons could act to extract salience.
Multitude of selection mechanisms in BG.
Have all these systems potentially fighting for output competing for expression in a central arena which decides how to allocate the finite motor resources

Question 5

BG dysfunction

Answer 5

All clues to how the BG functions come from its disorders and their symptoms e.g.
Individuals can either produce too many movements (PD) or too few (Huntington’s) suggesting the BG is a centre for movement selection to some extent and that it mediates the control of action selection

Question 6

Evidence for action selection hypothesis

Answer 6

BG is centrally located and receives inputs from all over the brain.
There must be some mechanism in the BG to be able to switch on selected resources (disinhibition gating hypothesis).
There must be some way behavioural subsystems asking for expression from the BG and how this translates to motor expression (connectivity).
The BG must be able to extract the urgency of each request - the request shouting the loudest gets the expression (intrinsic connectivity of striatum).
There must be evidence of neuronal selection mechanisms in BG.

Question 7

Disinhibition gating hypothesis and Alexander et al (1990)

Answer 7

Seems to be involved in release that comes from relief of tonic inhibition
Seems intrinsic to BG
This study injected glutamate into striatum
Striatum is inhibitory so when it’s inhibited by glutamate there’s an increase in activity releasing the structure from tonic inhibition
This causes reduced activity in output structures which releases the brain regions they’re projecting ro

Question 8

BG loops

Answer 8

Five main loops:
Motor
Oculomotor
Prefrontal 1
Prefrontal 2
Limbus
Different areas of the body are individually involved in their own loop which goes through the BG, all kept separately

Question 9

Intrinsic connectivity of striatum - sapience extraction in striatum

Answer 9

This allows neurons to be aware of how important the incoming requests are.
Spiny projection neurons are easily able to detect the loudest input by pattern matching to command request to extract the salience

Question 10

Multiple selection mechanisms in BG

Answer 10

Different levels of BG seem to favour selection - idea of this is intrinsically built into neurons and structure e.g.
Up-state/down-state filtering - when have activity in one area it turns off activity in adjacent area