But what I did not—and at the time could not—explain was exactly how or why. After all, according to the model, psychotic and autistic disorders are opposites, and so should never be found as pathologies in the same person!
As Abu-Akel and colleagues point out in the report on which my previous post was based, even though schizophrenia spectrum disorders (SSD) and autism spectrum disorders (ASD) are considered distinct conditions, there is evidence for an overlap between ASD and BD:
To date, the majority of reports of ASD-BD comorbidity are in ASD samples, with prevalences ranging from 6% to 21.4% (…). Only two studies have assessed ASD in BD samples: in youths (aged 7–17 years, N=157), 30% met diagnostic criteria for ASD (…); and in a small sample of adults (N=56), 50% had high levels of autistic traits as measured with the Social Responsiveness Scale (…).
Indeed, a self-report which illustrates the indisputable co-occurrence of ASD and BD was included in my book, The Imprinted Brain:
I have … an immense difficulty with maintaining eye contact in conversation: when I look at somebody speaking to me I almost become lost and I have difficulties processing what they are saying; I have similar difficulties putting together my thoughts if I am supposed to be looking at somebody, such as my therapist or psychiatrist. As a result, I do not have a strong sense of an emotional self, and I believe I resemble my dad in this manner, who does not emote very often. When I become manic, I suddenly feel comfortable engaging with people in conversation. These episodes always feel like miracles and lead to my thinking I have answers to all of life's problems and am the second coming of Jesus, which I understand is similar to a thought disorder that people with schizophrenia have. (p. 96)
As this autobiographical account suggests, ASD involves deficits in mental modules and brain centres involved with reading other people’s minds, such as gaze monitoring, conversation and social skills, interpreting body language, and so on. According to the diametric model of mental illness, other SSDs, such as paranoid schizophrenia, feature the opposite, in this case, over reading of other people’s minds in relation to their intentions towards you: negative ones in delusions of persecution, but positive intentions in erotomania (the erroneous belief that others are in love with you).
BD, however, is a disorder of what you might call intra-psychic mentalism: in other words, reading of your own mind. Normally, we read our own mental states by way of sensing our moods, thoughts and feelings in relation to something, and report these to others with phrases like I feel like Y; I'm in the mood for X; or, I'm happy with Z. In BD these internal mind-readings become pathologically exaggerated into crippling swings from mania to depression, often combined with delusional ideas about the self, messianically megalomanic or suicidally self-critical as the case may be: intra-psychic hyper-mentalism in fact.
The mental modules and brain circuits involved in reading your own mind are obviously somewhat different from those involved with reading other people’s minds. There is no way that you can directly feel other people’s emotions or gut-reactions the way you do your own, and reading them indirectly from a person’s expressions and behaviour can be very challenging at times, even for an expert mentalist. And clearly, if this is so, then ASD-BD co-occurrence is no longer a perplexing paradox for the diametric model: it is simply a question of some people being at the autistic end of the continuum of mentalism when reading other people's minds, but being at the psychotic end when reading their own thanks to different brain centres being active in each.
Nor is it necessarily paradoxical that geniuses such as Vincent Van Gogh (left), Hans Christian Andersen, and Emily Dickinson, have posthumously been diagnosed as bipolar by some authorities, but as autistic by others. In a previous post I commented on the surprisingly high incidence of BD among artists and especially poets. The intra-psychic hyper-mentalism of BD might enable artists of genius—and perhaps writers and poets in particular—to express their thoughts and feelings with unprecedented power and perceptiveness. According to the diametric model, genius is a rare co-occurrence of both autistic and psychotic savantism in the same person. If this is so, both those who diagnosed BD and those ASD in these cases may well have been correct after all.
Proof of the pudding will have to come from brain-imaging, and here the prediction is very clear: if the diametric model is correct, imaging should reveal mentalistic deficits in brain centres involved with reading other people’s minds in ASD but mentalistic hypertrophy in those involved with reading your own in BD. Indeed, and as I noted in the previous post, where the latter is concerned some such evidence has already been found in relation to the default mode network, which is associated with mentalistic cognition and reportedly with "hyper-connectivity" in depressives by contrast to the opposite finding in autistics.
(With thanks again to Ahmad Abu-Akel for his help.)