Editorial
‘Theory of mind’ and the prefrontal cortex
Ten years ago there was little knowledge of the functions of
the subregions of the human prefrontal cortex (see Fuster,
1989). Over the last 10 years there has been a great change
in the amount of information available on the topic. The
major source has been functional imaging. The journals now
contain a flood of studies on a variety of different types of
task where there are significant differences in activation in
complex patterns across prefrontal regions. Thus, a process
such as episodic memory (autobiographical memory),
previously thought not to be strongly related to frontal
functions, now seems to involve five, if not six, anterior
regions, which are differentially involved depending on subtle
variations in the tasks (see Henson et al., 1999; Lepage et al.,
2001). This suggests that a large number of different types
of subprocesses are frontally localized.
This flood of information has not, however, led to much
closure on the nature of the individual processes involved.
The difficulties involved in interpretation may be at least
twofold. The first is that the subprocesses involved may be
much too abstract to map simply onto the perceptual input
or motor output. Secondly, the tasks which activate prefrontal
cortex effectively may often involve a number of such
subprocesses and there may be no simple observable
manifestations of the successful completion of any one stage
in normal performance.
If these difficulties do exist, then progress will be
considerably quicker if functional imaging of standard tasks
can be supplemented by other methods. One would be to
employ apparently more complex tasks which, however, are
directly linked to more abstract potential subfunctions. The
second is to resurrect the older lesion approach, as the effects
of a lesion to an underlying process can be more transparent
to interpretation than are the patterns of activation obtained
when scanning normal subjects. However, to be usefully
relatable with imaging studies, an anatomically based group
study approach must use a finer localization grain than that
typical of 10 years ago. How lesion sites should be clustered
to form subgroups is a complex methodological problem.
The Toronto–Boston collaboration of Stuss, Alexander and
co-workers has been developing a number of alternative
patient grouping strategies over the last few years. Their
approaches have shown the importance of medial frontal
structures in standard frontal tasks such as Wisconsin Card
© Oxford University Press 2001
Sorting and Verbal Fluency, previously generally thought to
involve principally dorsolateral regions (see Stuss et al.,
2000). In the study of Stuss and colleagues in the present
issue, they contrasted a bifrontal group with left and right
frontal groups, with the bifrontal group overwhelmingly
having relatively pure medial lesions and they supplemented
the overall analysis by a ‘hot spot’ one (Stuss et al.,
2001). Again, the most striking finding involves the medial
prefrontal region.
The tasks they were studying involve ‘theory of mind’ or
‘mentalizing’, the cluster of abilities held to be necessary to
understand the mental processes of others. Originally
discussed by Premack and Woodruff, it was the demonstration
by Baron-Cohen and colleagues of their selective impairment
in autism that made it plausible that they have a specific
brain basis (Baron-Cohen et al., 1985), which more recent
studies have directly investigated (see Frith and Frith, 1999).
The first study to specifically investigate patients with frontal
lesions, that of Stone and co-workers, suggested that inferior
medial damage was critical (Stone et al., 1998). These authors
also found deficits following dorsolateral lesions but held
that working memory demands could be responsible.
However, they included no unilateral right frontal patients.
A very recent study again found a left frontal effect in
understanding ‘theory of mind’ stories (Channon and
Crown, 2000).
The current paper uses two main tasks. Both require the
patients to make an inference about the location of a ball or
a coin they cannot see, from the direction in which
experimenters point. In the first task there are two
experimenters who point to different places. The patients need
to realize that, as they are sitting next to one experimenter, this
person cannot see either possible position of the ball. Thus
the patient should rely on the pointing of the other
experimenter. The frontal patients produced a much higher
error rate on the task, so it is now clear that the frontal lobes
are important in mentalizing. It appeared that the right frontal
lobe was the most critical region; however, the small numbers
in that subgroup make this only a suggestion.
The second task involved deception. Here there is only
one experimenter who points. In this case, though, she/he
always points to the wrong position. It is this task that gives
rise to the striking right medial prefrontal difference between
248
Editorial
localization (within the hemisphere) using two very different
methodologies for establishing the material basis of certain
complex but critical higher-level cognitive processes.
Tim Shallice
Institute of Cognitive Neuroscience,
University College London,
London, UK
References
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Fig. 1 Location of peak activations in medial prefrontal regions
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