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111 | 2012
Annuaire du Collège de France 2010-2011
Résumé des cours et travaux 111e année
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Social Cognitive Neuroscience: Part 2

Chris Frith
p. 883-885

Notes de la rédaction

Les conférences de Chris Frith sont disponibles en ligne en format vidéo : http://www.college-de-france.fr/site/stanislas-dehaene/guestlecturer-2011-05-25-17h00.htm

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Mechanisms of Theory of Mind

1Theory of Mind or Mentalising is the ability to make inferences about the mental states of others: their intentions, desires and beliefs. Many studies have used brain imaging to explore the neural basis of this ability and the results are remarkably consistent. Activity is seen in medial prefrontal cortex (mPFC), in the superior temporal sulcus at the junction with the parietal lobe (STS/TPJ), and also in the temporal poles and the posterior cingulate cortex. But before we can make sense of this circumscribed brain system we need some idea of the mechanisms that underlie mentalising.

2A major clue to the intentions of others comes from the movements that they make. One proposal is that, by covertly simulating these movements using the brain’s mirror system, we can directly infer the intention behind them. However, this bottom-up mechanism cannot cope with the problem that the same movement may reflect different intentions. We have suggested that this problem is solved using the same mechanism, predictive coding, that is used to resolve ambiguities in sensory perception. This is a top-down mechanism which starts with a prior hypothesis about the likely intention of the actor given the current context. The brain’s mirror system is then used to predict the most likely movement given this prior hypothesis. Any discrepancy between the predicted and the actual movement observed provides a prediction error that can be used to update the hypothesis about the intentions of the actor. A number of studies suggest that activity in STS/TPJ reflects the magnitude of this prediction error. This seems to be the case even when intentions are inferred from cues other than movements.

3This mechanism is a one-way process in which an observer infers the intentions of an actor. In most human interactions, however, there is a two-way process in which two actors infer each other’s intentions. We refer to this as ‘closing the loop’. In this setting it is not enough for actor A to infer the intentions of actor B. Actor A must also infer what actor B has inferred about actor A. Such recursive inferences are particularly important for collaborative endeavours captured in games such as J.-J. Rousseau’s stag hunt. In this game a large reward can be obtained if both players choose to hunt the stag. However, this cooperation depends on player A believing that player B believes that player A will cooperate, etc. Thus, cooperation depends upon a depth of recursion sufficient to generate common knowledge that cooperation will occur. Brain imaging studies suggest that activity in mPFC may reflect prediction errors relating to inferences about the depth of recursion in social interactions. This places mPFC at the apex of a Bayesian hierarchy of top-down control of social cognition.

Understanding the symptoms of schizophrenia

4Schizophrenia is severe disorder affecting about 1% of the population and causing much distress to sufferers and their carers. Although there is strong evidence for a biological basis for the disorder, the diagnosis is still made on the basis of symptoms, which typically include hallucinations (false perceptions) and delusions (false beliefs). Over the last several years my aim has been to try and understands these symptoms at the cognitive, at the neural and also at the experiential level: what is it like to experience such symptoms.

5Many of the first rank symptoms of schizophrenia seem to reflect confusion between effects caused by the self as agent and effects caused by external agents. Examples are hearing one’s own thoughts being spoken aloud, or believing that alien forces are causing one’s actions. This latter experience, labelled a delusion of control, has been extensively studied. This symptom is not primarily a disorder of the control of action, but a disorder in the awareness of action, in particular in the sense of agency. An early idea was that this is a problem of self-monitoring. The patient is unaware of his intentions due to a failure of the corollary discharge (or re-afference copy) indicating that a movement is about to occur. As a result the movement is experienced as caused by external forces.

6More recently this idea has been expressed in terms of a forward model. When we perform an action, we predict the consequences of the action in terms of its behavioural and sensory effects. There are many experiments giving results consistent with the idea that patients with delusions of control are failing to make such predictions. At the neural level this is associated with failure to damp down neural activity reflecting the sensory consequences of self generated movements. The implication of these observations is that, for a patient with delusions of control, an active movement does genuinely feel like a passive movement.

7In the last few years there have been new developments in our understanding of the basis of the sense of agency for action. This depends in part on prediction and in part on the outcomes of action. Patients with delusions of control seem to be excessively influenced by outcomes, presumably because of failures of prediction. All these ideas about the symptoms of schizophrenia fit nicely into a Bayesian framework in which perceptions are generated through prediction and different sources of information are weighted on the basis of their reliability. I shall consider whether we can use this framework to construct a more general account of the symptoms of schizophrenia. In a Bayesian system there is no genuine distinction between delusions and hallucinations since both perceptions and beliefs are generated from the combination of prior hypotheses and new evidence. Prediction errors play a key role in this system. In relation to schizophrenia, one possibility is that the problem lies in the generation of prediction errors. If the prediction errors were false then the updating of perceptions and beliefs would no longer lead to models with a better fit to reality. Instead discrepancies would increase and this would lead to more and more radical reconceptualisations of what the world was really like. Perhaps this is what it is like to experience the symptoms of schizophrenia.

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Référence papier

Cours et travaux du Collège de France. Annuaire 111e année, Collège de France, Paris, avril 2012, p. 883-885. ISBN 978-2-7226-0156-7

Référence électronique

Chris Frith, « Social Cognitive Neuroscience: Part 2 », L’annuaire du Collège de France [En ligne], 111 | 2012, mis en ligne le 22 novembre 2013, consulté le 24 avril 2018. URL : http://journals.openedition.org/annuaire-cdf/1781

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Auteur

Chris Frith

Professeur au College University, Londres (Royaume-Uni). Institute of Cognitive Neuroscience

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Droits d’auteur

Collège de France

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