Is Theory of Mind dependent on episodic memory?

The latest issue of Science brings an article about the relationship between Theory of Mind (ToM) and episodic memory. The article abstract by Shanya Rosenbaum and her colleagues says:

[ToM] to infer other people’s current mental states and episodic memory of personal happenings have been assumed to be closely related. We report two participants with severely impaired episodic memory who perform indistinguishably from healthy controls on objective ToM tests. These results suggest that ToM can function independently of episodic memory.

In other words, it seems that ToM and episodic memory are independent processes. I, for one, first stumbled on why this relationship should be obvious at all. So let’s ask: why should we assume that there is a relationship between the two functions? In order to answer this, we first need to know what the two functions are.

ToM is actually a term that covers many different meanings, but for the present purposes (and this the presently most used meaning) ToM is taken to mean “the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires and intentions that are different from one’s own”. This original definition stems from the very beginning of ToM research, when Premack and Woodruff (1978) asked whether chimpanzees have a theory of mind. Later, Simon Baron-Cohen and colleagues (1985) asked whether ToM could be found in autistic children, and some even question whether ToM can be found in non-mammals such as birds.

So basically, ToM refers to our ability to think that others have thoughts and feelings that are different from our own. Importantly, neuroimaging studies by researchers such as Chris Frith and Rebecca Saxe, ToM have shown a relation to activation in medial frontal cortex, temporal poles and the temporoparietal junction.

Episodic memory refers to the memory of personally experienced events, which includes experienced places, associated emotions, and, to some extent, conceptual knowledge that is related to these experiences. Together with semantic memory, episodic memory has been thought to be a part of a declarative memory system, i.e., conscious memory. Episodic memory is normally associated with the medial temporal lobe (MTL). Most early theories stressed the importance of the hippocampus, but more recent research has pointed to additional regions within the MTL, such as the perirhinal cortex, parahippocampal cortex and entorhinal cortex (Moscovitch et al. 2006). In addition, have demonstrated hemispheric asymmetries during different stages of episodic memory. For example, encoding has been found to involve left hemisphere structures – both in the MTL and in prefrontal cortex – while retrieval has been shown to involve the right hemispheric counterparts more (Habib, Nyberg & Tulving, 2003).

So what is the relationship between ToM and episodic memory? The neural foundations suggests that they are separate processes. However, as Rosenbaum et al. writes:

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. The ability to consciously recollect past personal happenings has been shown to be necessary for imagining coherent and detailed personal happenings in the future. Both episodic memory and ToM emerge close in time in ontogenetic development. The neural substrate on which the two abilities rely is in many ways strikingly similar.

In order to study this relationship, the authors studied two patients that have well-described deficits in episodic memory. In particular, the patients had lost the ability to consciously recollect personal happenings from their own lives. The question now was: would these patients also show deficits in ToM? Using a comprehensive battery of tests on ToM (Bird et al. 2004), the patients and 14 control subjects were assessed for their ability to reason about other people’s thoughts and feelings. Here the researchers found that the ToM scores were indistinguishable from that of the control subjects.

Thus, this study demonstrates that episodic memory is not needed for normal ToM functioning. However, one should bear in mind that the study was made on subjects that have already a mature ToM (and premorbid episodic memory). Thus, it is still possible that a healthy episodic memory is important in the establishment of normal ToM function during development. It would indeed be interesting to see studies relating early damage to the MTL region and the development of ToM.

Copyright © T.Z. Ramsøy

Thomas Z. Ramsøy is a cognitive neuroscientist at the Danish Research Centre for Magnetic Resonance in Copenhagen, Denmark. He is also co-editor of SCR and BrainEthics.

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References

Baron-Cohen, S., Leslie, A.M., & Frith, U. (1985) Does the autistic child have a ‘theory of mind’? Cognition, 21, 37-46

Bird C. M., Castelli F., Malik O., Frith U., Husain M. (2004). The impact of extensive medial frontal lobe damage on ‘Theory of Mind’ and cognition. Brain, 127(Pt 4): 914-28

Habib R., Nyberg L., Tulving E. (2003). Hemispheric asymmetries of memory: the HERA model revisited. Trends Cogn Sci. 7(6): 241-245

Moscovitch M., Nadel L., Winocur G., Gilboa A., Rosenbaum R.S. (2006) The cognitive neuroscience of remote episodic, semantic and spatial memory. Curr Opin Neurobiol. 16(2):179-90.

Premack, D. G. & Woodruff, G. (1978). Does the chimpanzee have a theory of mind? Behavioral and Brain Sciences, 1, 515-526