Greg Detre
Sunday, March 02, 2003
set by Cynthia Breazeal
The two
assigned readings are the paper by Gallese and Goldman relating mirror neurons
to simulation theory of ToM, and the Williams et. al. paper relating mirror
neurons to imitation and autism.
For your
reading enjoyment and further background is the Arbib paper that Kai-yuh
mentioned in his presentation last class.
�� the activity of F5 neurons is correlated with specific hand and mouth motor acts and not with the execution of individual movements like contractions of individual muscle groups. What makes a movement into a motor act is the presence of a goal.�
By talking in terms of motor acts and goals, they believe that this allows one to see how the motor system could play a role in mental states like purpose or intention.
They noted grasping (especially for the precision prehension grip), holding, tearing and manipulation neurons.
These seem to be separated into grasping with the hand and grasping with the mouth.
Mirror neurons (MNs) fire both when the monkey sees an action performed, and when it performs the same actions.
They failed to respond to just the sight of the object or of the agent alone, nor to mimicking the action without the object or with tools.
Gallese and Goldmain claim that there�s good evidence to suppose that a similar execution/observation matching system exists in humans. I didn�t fully understand their description of Fadiga et al.�s Transcranic Magnetic Stimulation study. It showed that while observing objects being grasped, people�s motor evoked potentials in hand muscles increase during TMS. As far as I can tell, they are arguing that this is because the TMS stimulates the motor cortex, the MNs are responsible for increased activity in the premotor cortex, and in conjunction these responses affect the MEPs in the hand muscles. Two further PET studies have shown the left superior temporal sulcus (Brodmann�s area 21), the left inferior parietal lobule (Brodmann�s area 40) and the anterior part of Broca�s region (Brodmann�s area 45) to be particularly activated when observing being grasped rather than just the objects. This is one source of the argument for F5 being a homologue to Broca�s area.
see pg 11 in Williams et al.
Gallese & Goldman argue against MNs� role in learning by imitation, but instead as being implicated in mind-reading (aka �folk psychologising�), the activity of representing specific mental states of others. They discuss the difference between the theory theory and simulation theory of mind. Theory theory considers that people mind-read by creating theoretical posits of others� mental states in order to explain their behaviour, in the same sort of way �that physicists appeal to electrons and quarks to predict and explain observable phenomena�. The simulation theorists argue that humans� mind-reading abilities are based on the ability to simulate the mental states of others. In other words, we are able to predict or retrodict another person�s mental states by putting ourselves in another�s shoes and simulating what mental state we would be in.
If the brain is utilising the same machinery for making one�s own decisions as for predicting/retrodicting others� mental states offline (as per the simulation theory), then finding neurological evidence for mental mimickry in the mind-reading process would support the ST over the TT. They postulate that externally-generated activity in the MNs plays this simulation role, or at least some primitive version of it in monkeys. They consider Fadiga et al.�s TMS study to provide further support for the ST, since it showed that downstream motor activity in the observer is facilitated by observation of that motor activity in the target. This result is unexplained by the TT, and implies that the simulation activity is not completely offline in humans. That there exists a group of prefrontal-lesioned compulsive imitators could be neatly explained by a lack of downstream inhibition of this partially-online simulation process.
consider concluding paragraph
canonical neurons = activated during observation of graspable objects
interesting, implying a categorisation of objects into functional categories (that is, according to what you do with them), right???
precision prehension grip = prehension of small objects by opposing the thumb and the index finger
Tomasello�s three criteria for imitational learning:
1. the imitated behaviour should be novel for the imitator
2. it should reproeduce the behavioural strategies of the model
3. it should share with it the same final goal
Otherwise, behaviour should be explained in terms of stimulus enhancement, emulation or response faiclitiation.
In contrast, Byrne and Russon argue that imitation can be at the action-level or the program-level (which they argue may occur in non-human primates).
pg 499 � interesting references on primate social organisation
Hauser on deception
Stammbach on modified social hierarchies when less-dominant primate males were privy to information about how to use a lever to gain food
Heyes, and Byrne, on the possibility of mentalistic behaviour in primates
concluding paragraph:
�Our speculative suggestion is that �cognitive continuity� exists within the domain of intentional-state attribution from non-human primates to humans, and that MNs represent its neural correlate. This continuity is grounded in the ability of both human and non-human primates to detect goals in the observed behaviour of con-specifics. The capacity to understand action goals, already present in non-human primates, relies on a process that matches the observed behaviour to the action plans of the observer. It is true, as pointed out by Meltzoff and Moore, that the understanding of action goals does not imply a full grasp of mental states such as beliefs or desires. Action-goal understanding nevertheless constitutes a necessary phylogenetic state within the evolutionary path leading to the fully developed mind-reading abilities of human beings.�
Not only can the person execute
handwritten signatures consistency but can use chalk to sign the name in large
letters on a blackboard producing a recognizably similar appearance. The
individuality of the signature remains whether using the fine control of the
hand or the recruiting the large shoulder and arm muscles not normally required
for the task. Reproduction of recognizable movements occurs from preprogrammed
control patterns stored in the brain and recruited
Subjects wrote their signature with
their dominant index finger and ipsilateral big toe. fMRI showed that movement
parameters for this movement are stored in secondary sensorimotor cortices of
the dominant hand. These areas can be accessed by the foot and are therefore
functionally independent from the primary representation of the effector.
[Rijntjies et al. 1999]
what�s the difference between F4 and F5???
what did they previously think that these areas were for???
they�re near the premotor cortex, right???
is there a link between MNs, motor acts, intention and the parietal cortex (cf Andersen)???
are there �grasping neurons� that fire for either hand or mouth???
seemingly not � see pg 495
what sort of actions do the MNs respond to???
are they all hand- and mouth-related???
are there different ones for different actions???
are there any higher-level actions, e.g. grooming, cracking nuts etc.???
Deb mentioned something about MNs that do respond to the action being performed with tools � is that in the Arbib article???
in Fadiga et al.�s TMS study, why did they choose the dimming of the light as one of the controls??? is it something to do with attention???
is there any reason to believe that human MNs do anything different, extra or more specific than the MNs in monkeys???
I wouldn�t be at all surprised to find that humans have MNs that respond to imagined or intended actions� kind of in the same way that bits of V1 fire during dreams and imagined scenes, right???
if you believe in theory theory,
wouldn�t you expect people�s understanding/interpretation of others to
different from the mental state they experience themselves???
how would theory theory actually work???
same as all common sense and theory-formation � relevance-based search of some kind�???
do you ever see �internally-generated activation of the MNs� (pg 497)???
look at Box 2
neural correlate vs neural substrate
They characterise the autistic spectrum disorders in terms of impairments in social interaction, imaginative ability and repetitive and restricted patterns of behaviour. Autism has an onset before 3 years and is associated delayed/abnormal language development.
Baron-Cohen et al. suggested that autism may result from a deficit or delay in development of theory of mind. Williams et al. give three good reasons for thinking that this cannot be quite the right or whole story:
Rogers and Pennington first suggested that deficits in imitation might play this precursor role in the development of autism, and be able to answer at least the first two of the above objections. They suggested that the root of autism may be �impaired formation/co-ordination of specific self-other representations� resulting from impaired imitation. After all, intuition and the attribution of mental state both �involve translating from the perspective of another individual to oneself�. The link between the two is even closer for the simulation theory. Meltzoff and Gopnik even describe one way in which a new-born�s capacity for translating and imitating the seen behaviour (facial expressions) of others might underlie emotional mind-reading. Moreover, the 21 experimental studies of the imitative competence of individuals with autism seem to provide fairly strong evidence of impairment.
Imitative dyspraxia has been observed in patients with left frontal lobe lesions.
This impairment appears to be supra-modal
that is, to affect the replication of gestures oneself or on a mannequin.
no � between vision + motor
The functional significance of mirror neurons
supramodal
Rizzolatti and Arbib�s suggestion that monkey hand-action MNs may have evolved to subserve speech in humans by building upon a prelinguistic grammar of actions in the primate brain is interesting.
�By acting as a bridge between perceived and performed action and speech, the MN system is thus suggested to have provided the foundations for the evolution of dialogue. Furthermore, if MNs do process auditory representation as they do visual ones, they may be important in representing the relationship between words and the ir speaker like the personal pronouns.�
However, vervets have a roughly 4-signal verbal vocabulary, and bonobos chatter amongst each other in large groups for hours at a time. I would want to see how well Rizzolatti & Arbib�s suggestion fits with neural activity during these kinds of pre-linguistic behaviour.
MNs may be an important link between the prdouction and perception of speech (motor theory of speech perception) � see pg 12
They consider that emotional contagion and emotional mind-reading may be related (cf Meltzoff & Gopnik) � �since emotional states are closely linked to certain facial expressions, observation of a facial expression might resul tin mirrored (but mainly inhibited) pre-motor activation in the observer and a corresponding �retrodicted emotional state��.
�close connections between STS neurons, the MN circuits and the amygdala�
Shared attention may also be crucial to the development of a full ToM.
However, there is little evidence of imitation in monkeys, so maybe (see Gallese & Goldman) MNs are facilitating social understanding of others???
�fMRI with human subjects during a simple imitation task did indeed find activation in area 444 as well as in parietal cortex, suggesting that the MN is involved in imitation in humans�
Some impairment or delay in the development of (some of the) mirror neurons may be implicated in autism.
development of self-other representations
consequent failure to develop reciprocal social abilities: e.g. shared/joint attention, gesturla recognition, language (especially social/pragmatic aspects), breakdowns in the development of empathy/ToM
they explain the repetitive/inflexible/stereotyped behaviour as something to do with perception-action linkage
also, the child may learn some of their high-level executive functions (also apparently impaired in autism) from others � program-level imitation
correspondingly, there appears to be a correlation between tests of ToM and executive function
simulation +
executive functions related? (pg 18)
neuroimaging mirror neurons + ToM�
predictions:
imitative deficits in early years for autistic children, especially imitation involving:
a coordinated activity between different modes of sensory input
different groups of action-coding neurons
self-other visual transformations
non-standard McGurk effects in autistic children
�???
�???
�???
concluding discussion
unanswered questions
�This [simulation-based mind-reading] capacity might have evolved from an action execution/observation matching system whose neural correlate is represented by a class of neurons recently discovered in the macaque monkey premotor cortex: mirror neurons�.
echolalia /Ek<schwa>U"leIlI<schwa>/ n.L19. [mod.L, f. Gk ekho echo + -LALIA.] The meaningless repetition of words and phrases, esp. as a sign of schizophrenia; repetition of speech by a child learning to talk.echolalic a. M20.
do you usually get all the feature of autism together, or can you sometimes get some without the others???
if the latter, that would seriously undermine the hypothesis that there�s a common upstream cause�
ceiling effects???
do MNs fire during imitation then???
see pg 14
mind-reading vs ToM???
modulation???
re inhibition and changing modes???
so what happens if you lesion infants chimps� MNs???
Baron-Cohen�s CHAT screening???
what would Baron-Cohen�s opinion about the MNs be???