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Brain imaging is the ultimate test of the diametric model of the mind because it can directly image activity in parts of the brain known to be involved with mentalism, notably the medial prefrontal cortex (MPFC) and the right posterior superior temporal sulcus (pSTS), along with the adjacent temporo-parietal junction (TPJ). Indeed, and as I pointed out in a previous post, brain imaging studies of these regions have already revealed hyper-mentalism in those suffering from a psychotic spectrum disorder (PSD) such as schizophrenia. But as a recently published study by Angela Ciaramidaro and colleagues points out, to date no functional magnetic resonance imaging (fMRI) study has directly compared autism and schizophrenia during a mentalizing task to test the model's prediction that autism spectrum disorder (ASD) corresponds to the exact opposite: hypo-mentalism.
To correct this omission and to address the diametric hypothesis, the authors of this study conducted an fMRI experiment in which participants had to infer different kinds of intentions: namely, private (1 person acting) and communicative (2 persons interacting) with a physical (non-intentional) condition serving as a control condition. Twenty-three right-handed patients (2 females) with ASD aged 14–33 years and mean IQ of 105.9 were compared with 18 right-handed individuals (4 females) with paranoid schizophrenia aged 14–32 years, and mean IQ of 101.4. Twenty-three right-handed typically developed (TD) control participants (4 females), aged 15–27 years, mean IQ 106.8 10.9), were recruited from the community.
The study revealed that patients with schizophrenia showed a decreased differential activation of the MPFC and bilateral pSTS which was driven mainly by increased activation during the physical control condition. As the authors point out, this is consistent with a “hyper-intentional” mode of cognition. For ASD patients, known for a more mechanistic cognitive mode, the researchers predicted reduced activation during the mentalizing condition, consistent with a “hypo-intentional” mode of cognition (diagram above).
In addition, two other predictions were tested. Based on previous results, the researchers report that they
hypothesized that differences in neural function would be evident primarily in more complex social (communicative) intention reading compared to more simple (private) intention reading. Furthermore, we aimed to explore whether the assumed differences between groups would also be reflected in opposed connectivity patterns of the right pSTS, a key region of intention attribution, with other hubs of the social brain.
The authors report that
In a task specifically designed for reading different kind of intentions, we observed group specific activation and connectivity patterns in and between key regions of the social brain in line with the hyper-hypo-intentionality hypothesis. These were apparent only during complex social interactive but not during simple mentalizing conditions.
They go on to speculate that, if hyper-intentionality leads schizophrenics to attribute intentions to objects, while hypo-intentionality leads sufferers from ASD to treat persons as objects, the result would look superficially the same: “In both cases, the stance toward persons and objects could be altered in a group specific way but the result may be the same: to handle persons and objects in a similar way.” At the very least, this is something that might explain why both autistics and schizophrenics have been regarded as suffering from similar mentalistic symptoms in the past, and once again underlines the importance and originality of this particular study in differentiating between them.
The authors add that, in line with the hyper-intentionality hypothesis, patients with paranoid schizophrenia seem to process information about physical processes on the neural level in a similar way to information about mental states, and conclude that “Such an ‘intention detector’ may become hyper-active in paranoid thinking…” By contrast, the ASD group also showed differences in activation within the right pSTS when inferring communicative intentions, leading the researchers to comment that “This finding is exactly what we predicted for ASD based on the hypo-intentionality hypothesis.”
The authors conclude that the group differences in brain activation and the results of their connectivity analyses are consistent with the idea that mind-reading problems in schizophrenia are due to “an overactive intention-detection module, whereas mind-reading problems in ASD are rather due to an underactive intention-detector module”—just as the diametric model proposes.
Ciaramidaro and her colleagues are to be congratulated for carrying out the first direct test of the diametric model of mental illness on both autistics and psychotics using brain imaging. Where these researchers have led, many others are sure to follow, and if they find the same, neuroscience will have a new paradigm, the revolution in psychiatry will finally have begun, and the end of the Middle Ages in psychotherapy will be in sight!
(With thanks to Angela Ciaramidaro for her help.)
