Discussion
The aim of the present study was to investigate two important aspects of
eye-gaze processing in euthymic bipolar patients. Specifically, the
ability to infer the mental state and intention of others from the eyes
(reading the mind in the eyes) and the tendency to follow the direction
of another individual’s gaze (social attention) were assessed. Results
showed that, compared to controls, euthymic BD patients performed
significantly worse on the reading the mind in the eyes test. On the
other hand, no significant differences in social attention were found on
the eye-gaze cueing tasks.
Problems of euthymic BD patient in inferring the mental state of others
from the eyes are of clinical concern as they are likely to play a
significant role in the social difficulties that this group is known to
be at risk for [3]. Indeed, the ability to understand nonverbal
information about emotion and intention are believed to be factors
necessary for an adequate social functioning [47]. However,
literature about theory of mind in euthymic patients as measured by the
reading the mind in the eyes test did not yield a consistent pattern of
results. While one study suggests that euthymic BD patients have lower
performance than controls [6], other shows no differences between
patients and controls [24]. Therefore our results are consistent
with the former study but in contrast with the latter. These discordant
results may depend on sample characteristics; as compared to our study
and that of Bora and colleagues [6], in the Martino and colleagues
study [24] patients had more years of education (11.77, 11.44, and
13.8 years, respectively) and they were characterized by shorter
duration of illness (15.31, 15, and 11.4 years, respectively).
Regarding social attention orienting, we did not find differences
between the groups. This result could be possibly explained by a
sufficient level of remission of social attention in euthymic bipolar
patients. However, since no previous study has investigated social
attention in bipolar disorder during mania and/or depression, these
findings could be alternatively attributed to the intact ability in BD
to follow the direction of another individual’s gaze. Further research
is necessary to shed light on this issue.
Our finding that euthymic BD patients had an impairment in the ability
to infer the mental state of others from the eyes, but a preserved
tendency to follow the direction of another’s gaze is consistent with
the current theory regarding fast and slow systems of social cognition
[48-50]. The fast system involves the superior colliculus, pulvinar
nucleus, and amygdala, which are sensitive to observed gaze directions,
emotion-related signals, social salient information, and sexually
dominated processes. The slow system, on the other hand, involves
several cortical networks that include the superior temporal sulcus,
frontal eye field, lateral intraparietal area, or other areas in the
frontal–parietal attention network. This slow system mainly processes
eye postures, face identity, intentionality, and other complex social
information. We suspect that the attentional orienting in response to
gaze cue may be involved in both fast and slow systems, whereas the
ability to judging mental state from the eyes may be involved only in
the slow system. Thus, the results of the present study might suggest
that euthymic BD patients are impaired in slow but not in fast systems
of social cognition. Consistent with this view are the evidence showing
during remission of BD a normalization of amygdala response [51, 52]
but an abnormal activity of brain areas normally implicated in the slow
system of social cognition such as the superior temporal sulcus [53]
and the ventrolateral prefrontal cortex [17-20] .
As in their original version, in the present study, we used pictures of
eye regions of the face and schematic face for the reading the mind in
the eyes test and eye-gaze cueing task, respectively. Therefore the
different results showed in the two test may be, at least in part, due
to the social meaningfulness of stimuli used. Maybe euthymic bipolar
patients are only impaired in processing photorealistic eye-gaze but not
schematic faces. There are evidence suggesting that that schematic face
and images of real faces are processed similarly evoking similar cueing
effects [54] and theory of mind / “socialness” [55, 56].
However, the impact of the different stimulus parameters has never
directly compared in euthymic bipolar disorder. Further research will be
necessary to shed light on this issue.