Nick lecture 4

P&C

M1 summary

•Motor pathways are crossed, left hemisphere moves muscles on the right of the body

•Neurons in primary (M1) operate single muscles

•M1 is topographically arranged, neighbouring neurons activate neighbouring muscles

premotor cortex summary

•Premotor cortex neurons provide input to several M1 cortical neurons

•Premotor cortex neuron activity causes movement in groups of muscles

•Activity in one neuron can generate coordinated action

grasping objects results: Umilta et al. (2008)

Action executed with 2 types of pliers is diff

M1 Neurons: Half responded to hand closure, half responded   to hand opening

Pre-motor neurons: All responded during grasping with either   pliers

M1 neurons coding the hand movements

Pre-motor neurons coding the Goal of the action

results: Fogassi et al 2005

•Neurons respond during movement 1

•But only when the movement 2 is appropriate

•mirror neuron responds selectively before the action happens

- This is NOT clairvoyance! (predicting what is about to come)

Mirror Neuron firing rate represents the INTENTION of the monkey to perform a specific action

arguments for humans NOT having mirror neurone

-Evidence is indirect

-Relies on correlations between visual and motor activity

-Neuroimaging is a measure of correlation

would need to do a single cell study of human mirror neurons

where did Mukamel et al. 2010 find evidence for human mirror neurons

Supplementary Motor Area

  Hippocampus

Respond to both observation and execution of actions (hand grasping & facial expressions)

perception of actions results: Jacobs & Shiffrar (2005)

Observers walking on a treadmill: found it difficult to judge Biological Motion walker speed

Observers cycling on an exercise bike: did not

Simulation Theory (Gallese & Goldman, 1998)

To understand other people’s actions we simulate their actions - using our motor systems

Theory Theory

We acquire and deploy a commonsense theory of mind – set of causal/explanatory laws

(I understand your actions because Ik what you guys do because I have learnt it over time- I am not simulating the movement)

Understanding action intention results: Iacoboni et al (2005)

Greater activity in premotor cortex to intention condition

Mirror neurons responsible for understanding the intention of the observed actor

Drinking, cleaning...

where are mirror neurons found?

premotor cortex

4. what is the MNS for?: what do Arbib & Rizzolatti (2001) suggest?

1.When an actor acts, the observer will recognise the action and the actor’s intention

2. development of the observer’s ability to consciously control their MNS results in the ability to emit a voluntary signal

3.A primitive dialogue is formed between observer and actor

What is the anatomical evidence that impaired MNS performance underlies ASD?

Hadjikhani et al (2006)   – Local thinning in the Cerebral Cortex in   areas belonging to the Mirror Neuron System (STS, IPL, IFG)

  - ASD severity correlated with cortical thinning

(Broken mirror neuron hypothesis- somehow MNS broken which leads to characteristics seen in ASD)

What is the physiological evidence that impaired MNS performance underlies ASD?

• Mu rhythm suppression – index of motor activation (Get a signal- as soon as you start to move, you get a reduction in mu rhythm= mu suppression)

• Occurs during observation of actions

• Reduced Mu Rhythm suppression in ASD

• Reduced TMS induced corticospinal activation during action observation

• In children – reduced MNS response to observation and execution of facial expressions in IFG