Mirror neuron system

What areas make up the motor cortex?

Primary motor cortex, supplementary motor cortex and premotor cortex

How can motor pathways in M1 be described?

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

How do neurons in M1 work?

• Operate single muscles

• M1 topographically arranged, neighbouring neurons activate neighbouring muscles.

• Homunculus, somatotopic map (e.g. bigger representation for hands)

What does premotor cortex do?

• Neurons provide input to several M1 cortical neurons

• Neuron activity causes movement in groups of muscles.

• Activity in one neuron can generate coordinated action. e.g. reaching

What are mirror neurons?

Essentially premotor cortex neurons

Which area of the brain have mirror neurons been found in?

F5

What do mirror neurons do in relation to motor and vision?

• Mirror neurons respond during execution of goal directed actions

• Mirror neurons respond to sight of the action

  

How do mirror neurons relate to action specificity?

• Respond during specific actions

• Respond to the sight of specific action

What was found in a study of action specificity (twisting of peanuts) in mirror neurons in premotor cortex?

• Respond to observation of experimenter twisting a peanut but only when anticlockwise rotation.

• Motor response only when monkeys twist anticlockwise. Direct matching of motor action onto sight of experimenter performing action.

How do mirror neurons in premotor cortex relate to face actions?

• Mirror neurons respond during movement of face.

• Mirror neurons respond to sight of face movements.

• Ingestive: grasping,sucking. Communicative mouth actions: lipsmacking, teeth chatter

What do mirror neurons do in relation to motor, vision and audition?

Respond during specific actions, sight of same action and sound of same action.

What did Kohler et al find in a test of different types of visual, auditory and motor actions and mirror neuron response?

• Cell 1 → High response to vision+sound, vision, sound and motor actions for peanut breaking. Lower response for ring grasping (control action).

• Cell 2 also responds selectively.

How do mirror neurons in premotor cortex relate to hidden actions?

• Respond during execution and observation of specific actions.

• Typically do not respond to miming.

• Many respond when the late part of the action is out of sight.

• Many mirror neurons respond when action cannot be seen, e.g. monkey must know object behind occluder.

• Might respond when they know outcome of specific action.

What did Umilta et al find in study of mirror neurons and miming actions?

• Neuron has high response when hand actually reaches and touches object.

• Mirror neuron doesn’t fire as well to miming action when miming to pick up object

What did Umilta et al find in study of mirror neurons and hidden actions (action to pick up block, both miming and real action hidden by sliding occluder)?

• Mirror neuron still responds in object condition despite not being able to see object.

• Mirror neuron doesn’t fire in imaginary condition despite both conditions visually appearing the same.

What did Umilta et al find in a test of the response of pre motor and M1 neurons during tool use where monkeys were trained to grasp objects with 2 types of pliers (normal and reverse, two different types of hand movement)?

• M1 neurons → half responded to hand closure, half responded to hand opening.

• Premotor neurons → all responded during grasping with either pliers.

• M1 neurons coding the hand movements. Premotor neurons coding the goal of the action.

• Premotor neuron discharge pattern for grasping transferred to tool use, tool incorporated into motor system as if it were artificial hand.

• F5 mirror neurons coding goal of action.

Where else have mirror neurons also been found in the brain of monkeys?

Posterior parietal cortex

What did Fogassi et al find in a study training monkeys to perform two different actions: 1. grasped food to eat it or 2. grasped object to place it somewhere. Then watch human experimenter perform same actions?

• Movement 1 always same, movement 2 based upon goal

• Neurons respond during movement 1 but only when movement 2 appropriate → responds before action actions

• Mirror neuron firing rate represents the intention of monkey to perform a specific action

What has been found in relation to STS and mirror neurons?

STS neurons respond selectively to actions.

STS neurons integrate sight and sound of actions

No one has found mirror neurons in STS, no motor response

What does TMS of M1 result in?

• Causes motor evoked potentials (MEPs) in muscles.

• MEPS provide metric of motor system activity.

• Increased input from visual system to motor system → increased activity in motor system.

• Action observation during TMS activation of M1 increases likelihood of MEPS.

What has been found in relation to MEPS and action observation?

• MEPs enhanced during action observation.

• Watching hand actions increases MEPs in hand → action specificity.

• Sounds also increase likelihood of MEPs

• Listening to words that use tongue enhance MEPs in subject’s tongue

What has been found in fMRI studies of the brain when executing hand, mouth and foot movements and observing these movements?

Similar regions in brain respond to both execution and observation of these movements. Overlapping activity.

Why has it been argued that humans do not have mirror neurons?

• Evidence is indirect

• Relies on correlations between visual and motor activity

• Neuroimaging is measure of correlation

• Only one cell study of human mirror neurons exists

Which areas of the human brain did Mukamel et al find evidence in the only single cell study for mirror neurons in?

Supplementary motor area and hippocampus

Respond to both observation and execution of actions

What was found in study of observation and execution of frowning actions?

What do some think the mirror neuron system is for?

action perception, action understanding, action sounds, touch, smell, imitation, mind reading, theory of mind, motor learning, empathy, language, autism, schizophrenia, dyslexia, etc

What did Hamilton et al find in study of ….

What did Jacobs and Shiffrar find in a study where observers walking on a treadmill or on exercise bike had to judge biological motion walker speed?

• Observers on treadmill found it difficult to judge walker speed.

• Observers cycling did not

How does mirror neuron system link to understanding actions?

• When we execute an actions, mirror neuron system is active

• We understand action that we are executing

• Perception of other people’s actions → activity in mirror neuron system. Therefore understand the action.

What is simulation theory (Gallese and Goldman)?

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

What is theory theory?

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

What did Keysers et al find in relation to mirror neurons for touch?

• Somatosensory neurons that respond during touch and observing another person being touched.

• Different neurons code touch in different places.

• Can empathise with person being touched but don’t actually feel touch

What did Ramachandran find in study of mirror neurons for touch when using nerve block in Brachial plexus?

• Will feel the touch.

• Skin provides barrier between your and other peoples mind

What did Lacoboni et al find in study of understanding action intention using context?

• Greater activity in premotor cortex to intention condition.

• Mirror neurons responsible for understanding intention of observed actor, drinking, cleaning.

What did Buccino et al find in study of brain activity in response to video of man lipreading, monkey lipsmacking and dog barking?

No response to dog

What did Arbib and Rizzolatti suggest about mirror neuron system and language?

• Mirror Neurons represent actions: for imitation and understanding. As such, they are a link between sender and receiver

• F5 in the monkey is responsible for hand and mouth movements: is the homologue of Human Broca’s area (speech area)

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

  2.The development of the observer’s ability to consciously control her/his mirror neuron system results in the ability to emit a voluntary signal

  3.A primitive dialogue is formed between observer and actor

What does Libermans motor theory of speech state?

states that this link between sender and receiver is a necessary pre-requisite for any form of communication

What is primitive dialogue in use for the mirror neuron system?

• Initial intentional communication was based upon hand movements

• Also: hand-mouth movements and oro-facial gestures

What is ASD associated with?

Impaired social and emotional skills

  Lack of empathy and engagement with others

  Impaired perception of emotions

What is the anatomical evidence that impaired mirror neuron system performance underlies ASD (Hadjikhani et al)?

• Local thinning in the Cerebral Cortex in   areas belonging to the Mirror Neuron System (STS, IPL, IFG)

• ASD severity correlated with cortical thinning

What is the physiological evidence that impaired mirror neuron system performance underlies ASD?

• Mu rhythm suppression – index of motor activation

• Occurs during observation of actions (Lepage & Theoret, 2006)

• Reduced Mu Rhythm suppression in ASD (Oberman et al 2005, Cole, Barraclough et al. 2017)

• Reduced TMS induced corticospinal activation during action observation (Theoret et al 2005)

• In children – reduced MNS response to observation and execution of facial expressions in IFG (Dapretto et al 2006)

What was found in study where children with ASD had to judge different types of facial actions and indicate emotion and brain activity?

• Activity in IFG declined with severity of ASD