Theory of Mind does not require episodic memory?

The ability to interpret others' mental states and intentions, called "Theory of Mind," has been a key area of interest for those studying the evolution of primate and human social behavior. Often, people have imagined that Theory of Mind emerges as a correlate of self-awareness -- the ability to reflect on one's own mental states. As the model goes, a focal individual interprets another's mental state by imagining herself "in the shoes of" the other individual.

Well, this week's Science has a short paper by R. Shayna Rosenbaum and colleagues that presents evidence that the "in their shoes" model is wrong. First a mini-review of why you would believe the usual idea in the first place:

The idea that ToM is closely related to, and that it may depend on, episodic memory and autonoetic consciousness seems perfectly natural: that in order to imagine and make sense of other people's thoughts, feelings, intentions, and actions, we must rely on our autobiographical recollections (1). The ability to consciously recollect past personal happenings has been shown to be necessary for imagining coherent and detailed personal happenings in the future (2, 3). Both episodic memory and ToM emerge close in time in ontogenetic development (4). The neural substrate on which the two abilities rely is in many ways strikingly similar (1).

But they examined two patients with brain injuries that eliminated personal episodic memory. In both cases, the patients showed an ability to interpret the mental states of other individuals, even though they could not imagine future events in their own perspective:

The current findings are at variance with the idea that the ability to simulate or reconstruct one's own past mental states is necessary to imagine the contents of other people's minds (1, 2). Both K. C. and M. L. suffer from severe difficulties in consciously (autonoetically) recollecting any events from any period of their lives. Yet they have no apparent difficulty in taking other persons' perspectives and inferring other people's thoughts, feelings, and intentions, as revealed by the ToM tests. The findings imply that K. C.'s and M. L.'s ToM ability may depend on semantic memory and general knowledge abilities that are largely preserved in both cases (5, 6).

This may go along with last week's paper by Hamlin, Wynn and Bloom, which showed that infants develop an ability to evaluate others' intentions much earlier than had been thought:

Here we show that 6- and 10-month-old infants take into account an individual's actions towards others in evaluating that individual as appealing or aversive: infants prefer an individual who helps another to one who hinders another, prefer a helping individual to a neutral individual, and prefer a neutral individual to a hindering individual. These findings constitute evidence that preverbal infants assess individuals on the basis of their behaviour towards others.

This isn't quite the same as Theory of Mind -- the infants are getting a general idea of whether a person is nice, not evaluating specific intentions. But the study of the individuals who lack episodic memory suggested that they were using more general cognitive resources to enable their interpretation of others' intentions. That would presumably include the kinds of heuristics that these babies were developing to judge people as "helpers" or "hinderers".

It may be that Theory of Mind is built from exactly the kind of simple observations that the babies can use, and that rather than build a detailed "simulacrum" of another person's intentions, we can interpret their likely intentions based on general knowledge of what people are likely to do based on similar external signs. That kind of skill might vary quantitatively among primate species, and provides a possible evolutionary pathway for this important social ability.

References:

Hamlin JK, Wynn K, Bloom P. 2007. Social evaluation by preverbal infants. Nature 450:557-559. doi:10.1038/nature06288

Rosenbaum RS, Stuss DT, Levine B, Tulving E. 2007. Theory of mind is independent of episodic memory. Science 318:1257. doi:10.1126/science.1148763