This is a gem of a paper. It provides a fresh look at the...
This is a gem of a paper. It provides a fresh look at the role of perception and cognition in development of schizophrenia from the vantage point of research on congenital or early (C/E) blindness. As reviewed by Silverstein and colleagues (Silverstein et al., 2012), there are no known cases of people with C/E blindness who developed schizophrenia. In a companion paper, they clarify that this does not appear to be due to the low base rates of either disorder (Silverstein et al., 2013).
The authors discuss evidence that C/E blindness confers protection against schizophrenia in a twofold manner. First, there are neuroplastic changes that produce compensatory enhancement of functions such as auditory perception and attention, memory (including working memory), language, and construction of subjective experience. In contrast, all of these functions are well known to be impaired in schizophrenia. A particularly interesting example of enhancement of subjective experience is improved serial processing in people with C/E blindness. This appears to be due to the reliance on haptic and auditory information, which leads to expertise in constructing gestalts of information acquired serially. This is in contrast to schizophrenia, where holistic gestalt processing is impaired, and there is no compensatory overdevelopment in serially constructed experience. The paper includes quotes from Helen Keller describing the feeling of putting the parts together. Silverstein and colleagues suggest that, for example, a learning style of enhanced sequential and controlled processing may lead to improved ability to integrate subjective experience and to improve working memory in C/E blindness.
A second protective factor is that people with C/E blindness do not suffer the deleterious developmental effects of impaired visual processing. These deleterious effects include the impaired multisensory processing and enhanced attention to detail, rather than the use of holistic processing, that are seen in schizophrenia. The authors speculate that lack of impaired visual processing in C/E blindness may protect against delusion formation that occurs as a result of aberrant sensory experience.
This is a data-driven paper that provides an excellent review of the literature. But it also generates hypotheses about the protective effects of neuroplastic changes in C/E blindness. The paper also discusses the consequences of aberrant visual perception in sighted people. Silverstein and colleagues suggest that the neuroplastic changes seen in C/E blindness may provide useful strategies for enhancing cognitive reserve in people at risk for schizophrenia.
Silverstein SM, Wang Y, Keane BP. 2012. Cognitive and neuroplasticity mechanisms by which congenital or early blindness may confer a protective effect against schizophrenia. Frontiers in Psychology. 3: article 624. Abstract
Silverstein SM, Wang Y, Roche MW. 2013. Base rates, blindness, and schizophrenia. Frontiers in Psychology. 4: article 157. Abstract
The comment by Pamela Butler on the review by Silverstein...
The comment by Pamela Butler on the review by Silverstein and colleagues is very important and timely. Both the paper and comment highlight the role of the visual system in the development of schizophrenia. As stated in the review, congenital or early (C/E) blindness does not confer protection from other mental disorders, while the opposite also seems true: no other sensorial deprivations have been associated with schizophrenia (Silverstein et al., 2012). The neuroprotective view constitutes a novel postulate that may have a direct impact on future interventions in the attempt to modify the course of the disease as early as possible. Likewise, if C/E blind people are protected against schizophrenia because of the absence of aberrant visual processing during neurodevelopment, we can infer that under this view, visual dysfunction should be present in schizophrenia as a sufficient condition to develop it. Thus, the visual system may become the most promising target to develop tools to distinguish schizophrenia across populations, as well as to understand the nature of the disease(s) (González-Hernández et al., 2006).
González-Hernández JA, Pita-Alcorta C, Cedeño IR. 2006. From genes to brain oscillations: is the visual pathway the epigenetic clue to the schizophrenia? Med Hypotheses 66: 300-308. Abstract
My research has uncovered cases of people with C/E...
My research has uncovered cases of people with C/E blindness who develop schizophrenia (Leivada and Boeckx, 2014).
Crucially, all cases involve blindness of a peripheral origin. No case of schizophrenia and blindness of a cortical origin has been uncovered. On the basis of the presented case reports, my co-author and I proposed a modulation of the protection mechanism, building on the presentation of the protective mechanism as this appears in the work by Silverstein et al. (Silverstein et al., 2013).
Leivada E, Boeckx C. Schizophrenia and cortical blindness: protective effects and implications for language. Front. Hum. Neurosci., 28 November 2014. Abstract
Silverstein SM, Wang Y, Keane BP. Cognitive and neuroplasticity mechanisms by which congenital or early blindness may confer a protective effect against schizophrenia. Front Psychol 2013. Abstract