Neural noise and cortical inhibition in schizophrenia

Abstract

Background: Neural information processing is subject to noise and this leads to variability in neural firing and behavior. Schizophrenia has been associated with both more variable motor control and impaired cortical inhibition, which is crucial for excitatory/inhibitory balance in neural commands. Hypothesis: In this study, we hypothesized that impaired intracortical inhibition in motor cortex would contribute to task-related motor noise in schizophrenia. Methods: We measured variability of force and of electromyographic (EMG) activity in upper limb and hand muscles during a visuomotor grip force-tracking paradigm in patients with schizophrenia (N ¼ 25), in unaffected siblings (N ¼ 17) and in healthy control participants (N ¼ 25). Task-dependent primary motor cortex (M1) excitability and inhibition were assessed using transcranial magnetic stimulation (TMS). Results: During force maintenance patients with schizophrenia showed increased variability in force and EMG, despite similar mean force and EMG magnitudes. Compared to healthy controls, patients with schizophrenia also showed increased M1 excitability and reduced cortical inhibition during grip-force tracking. EMG variability and force variability correlated negatively to cortical inhibition in patients with schizophrenia. EMG variability also correlated positively to negative symptoms. Siblings had similar variability and cortical inhibition compared to controls. Increased EMG and force variability indicate enhanced motor noise in schizophrenia, which relates to reduced motor cortex inhibition. Conclusion:The findings suggest that excessive motor noise in schizophrenia may arise from an imbalance of M1 excitation/inhibition of GABAergic origin. Thus, higher motor noise may provide a useful marker of impaired cortical inhibition in schizophrenia.

Breathing in waves: Understanding respiratory-brain coupling as a gradient of predictive oscillations

“…Aberrations in cortical E/I ratio are also highly prevalent in schizophrenia patients, e.g. in motor (Carment et al, 2020) and sensory systems (Molina et al, 2020). In line with these results, a recent MEG study by Phalen and colleagues (2020) highlighted distinct anatomical networks with altered resting-state alpha power in schizophrenia patients, including left temporal, right inferior frontal, right posterior parietal, and bilateral cingulate cortices -sites which are largely part of the RMBO network in neurotypical participants .…”

“…In schizophrenia, respiratory abnormalities such as irregular breathing patterns and reduced heart rate variability have been reported (Akar et al, 2012;Peupelmann et al, 2009). Altered respiratory physiology in schizophrenia might impact the neural oscillations, particularly in the gamma frequency range, which has been associated with perceptual and cognitive functions (Carment et al, 2020;Uhlhaas and Singer, 2013). This disruption in brainbreath coupling could lead to imbalances in precision-weighted prediction errors, contributing to the formation of hallucinations and delusions.…”

The effects of abnormal visual experience on neurodevelopmental disorders

“…Given that tilt aftereffects rely on excitatory/inhibitory dynamics between orientation-tuned cortical neurons, these findings of stronger tilt aftereffects could reflect excitation and inhibition imbalances. This has been supported by a large body of literature and is important in understanding the neurobiological impairments in schizophrenic brains (Carment et al, 2020;Sigurdsson, 2016;Thakkar et al, 2017;Yoon et al, 2010). Moreover, altered aftereffects can be contextualized within a Bayesian framework, in which perception is dictated by an interplay of a "prior" or a previous belief, and sensory information or the "likelihood."…”

Positional Stability of the Non-Dominant Hand is Associated with Difficulties in Daily Functioning in Schizophrenia

“…In addition, aberrant excitability in the motor cortex has been reported in patients with schizophrenia, regardless of whether they are unmedicated or medicated [33]. This hyperexcitability in the motor cortex leads to dis-turbances in motor control, suggesting decreased motor inhibition [34]. Stabilizing forearm posture against perturbation induced by a finger task demands the contraction of proper muscles and the suppression of inessential muscles due to sensory information.…”