Early somatosensory processing in individuals at risk for developing psychoses

Abstract

Human cortical somatosensory evoked potentials (SEPs) allow an accurate investigation of thalamocortical and early cortical processing. SEPs reveal a burst of superimposed early (N20) high-frequency oscillations around 600 Hz. Previous studies reported alterations of SEPs in patients with schizophrenia. This study addresses the question whether those alterations are also observable in populations at risk for developing schizophrenia or bipolar disorders. To our knowledge to date, this is the first study investigating SEPs in a population at risk for developing psychoses. Median nerve SEPs were investigated using multichannel EEG in individuals at risk for developing bipolar disorders (n = 25), individuals with high-risk status (n = 59) and ultra-high-risk status for schizophrenia (n = 73) and a gender and age-matched control group (n = 45). Strengths and latencies of low- and high-frequency components as estimated by dipole source analysis were compared between groups. Low- and high-frequency source activity was reduced in both groups at risk for schizophrenia, in comparison to the group at risk for bipolar disorders. HFO amplitudes were also significant reduced in subjects with high-risk status for schizophrenia compared to healthy controls. These differences were accentuated among cannabis non-users. Reduced N20 source strengths were related to higher positive symptom load. These results suggest that the risk for schizophrenia, in contrast to bipolar disorders, may involve an impairment of early cerebral somatosensory processing. Neurophysiologic alterations in schizophrenia precede the onset of initial psychotic episode and may serve as indicator of vulnerability for developing schizophrenia.

Early Somatosensory Processing Over Time in Individuals at Risk to Develop Psychosis

“…The previously reported analysis of the baseline data of the present at-risk sample showed that alterations of early sensory filtering as measured by SEPs were observable also at the at-risk level ( 15 ). Subjects at risk for psychosis showed reduced low- and high-frequency source activity compared to subjects at risk for bipolar disorders and reduced high-frequency amplitudes compared to healthy controls.…”

“…The aim of the present study was to explore the suitability of SEP as a neurophysiological marker. Therefore, we investigated the course of early sensory processing in help-seeking individuals being at risk to develop psychosis at the time of the baseline examination ( 15 ). Specifically, we distinguished between subjects remaining at risk at follow-up vs. subjects who converted to manifest psychosis during this time.…”

“…Low- and high-frequency components of SEPs measured at baseline and at follow-up 1 year later were analyzed in relationship to the clinical symptoms. Given that the previously reported differences in SEP measures at baseline were accentuated among cannabis non-users ( 15 ), we aimed to control specifically for the effect of cannabis in the present study, respectively, to explore SEP in cannabis-free subjects in case of an effect of cannabis in the whole group. We thought to find differences in SEP between converters and at-risk subjects as early as baseline, as it would be expected from a neurobiological marker.…”

Are cannabis-using and non-using patients different groups? Towards understanding the neurobiology of cannabis use in psychotic disorders

“…There appears to be some evidence for modulation in clinical high-risk groups of PPI: one study has paradoxically shown that PPI is increased in cannabis use verses healthy controls but decreased in at-risk mental state subjects (Winton-Brown et al, 2015). Other studies have failed to elicit differences between P-C and P-NC in somatosensory evoked N20, P25 (Hagenmuller et al, 2014), auditory oddball N100, N200, P200 and P300 (Van Tricht et al, 2013).…”

Atypical visual and somatosensory adaptation in schizophrenia-spectrum disorders

“…It is of considerable interest that a recent study has reported SEP deficits in a large group of individuals who were determined to be at very high genetic risk for developing schizophrenia, 103 further suggesting that somatosensory processing deficits may prove useful as endophenotypes for this disorder. Another recent study used the steady-state response technique to assess the inter-trial temporal stability of the cortical somatosensory response in SCZ, with results pointing to both reduced amplitudes and more variable phases of the steady-state response, 104 highly reminiscent of the early work of Shagass and colleagues.…”