Phase-Amplitude Markers of Synchrony and Noise: A Resting-State and TMS-EEG Study of Schizophrenia

Abstract

The electroencephalogram (EEG) of schizophrenia patients is known to exhibit a reduction of signal-to-noise ratio and of phase locking, as well as a facilitation of excitability, in response to a variety of external stimuli. Here we demonstrate these effects in transcranial magnetic stimulation (TMS)-evoked potentials and in the resting-state EEG. To ensure veracity we used three weekly sessions and analyzed both resting state and TMS-EEG data. For the TMS responses our analysis verifies known results. For the resting state we introduce the methodology of mean-normalized variation to the EEG analysis (quartile-based coefficient of variation), which allows for a comparison of narrow-band EEG amplitude fluctuations to narrow-band Gaussian noise. This reveals that amplitude fluctuations in the delta, alpha and beta bands of healthy controls are different from those in schizophrenia patients, on time scales of tens of seconds. We conclude that the EEG-measured cortical activity patterns of schizophrenia patients are more similar to noise, both in alpha and beta resting state and in TMS responses. Our results suggest that the ability of neuronal populations to form stable, locally and temporally correlated activity is reduced in schizophrenia, a conclusion that is in accord with previous experiments on TMS-EEG and on resting-state EEG.

The Role of Alpha Oscillations among the Main Neuropsychiatric Disorders in the Adult and Developing Human Brain: Evidence from the Last 10 Years of Research

“…The existing literature suggests that a faster (rather than slower) IAF entails better perceptual acuity and efficiency [ 38 , 78 ], with individuals displaying pronounced schizotypal traits characterized by slower IAFs [ 79 ]. Findings gathered over the last decade unilaterally uphold previous knowledge, namely slower resting-state IAFs in SSD patients [ 68 , 69 , 70 , 73 , 77 ], with the degree of deceleration positively correlating with visuo-attentional performance and scorings at cognitive scales [ 80 ]. Furthermore, faster IAFs in SSD individuals undergoing multisession cognitive training was found to predict protocol outcome (i.e., responders vs. non-responders).…”

“…However, recent evidence appears to depict a more nuanced portrait of the matter. While some studies described no reduction in terms of posterior alpha activity in SSD patients [ 68 , 69 , 70 ], one reported higher parieto-central alpha power in medicated patients as compared to healthy controls [ 71 ]. Such an increase was also outlined by data collected in three additional papers, focusing on, rather than task-positive regions (i.e., neural areas more active during attention-demanding tasks), task-negative areas, which are known to increase their level of excitability at rest [ 72 ].…”

Electrophysiological and Behavioral Effects of Alpha-Band Sensory Entrainment: Neural Mechanisms and Clinical Applications

“…Moreover, individuals with ASD also show alterations in long-range structural and functional alpha connectivity (rather than in a local area; [129,130]), with a prevalence of ascending connections from posterior to anterior areas, pointing to a tendency to convey more bottom-up information [117,129,131]. In the domain of SSD, instead, a consistent slowdown of IAF [130,[132][133][134][135][136] and a reduction in alpha power [137][138][139][140][141][142][143] has been observed, together with pervasive dysregulation in the way alpha oscillations instantiate phasic fluctuations and a reduction in long-range alpha coherence at rest and across different cognitive tasks [136,144]. In addition, alterations in alpha rhythm were shown to predict the structural and functional integrity of the visual system in patients affected by posterior brain damage.…”

“…• Slowdown of the IAF [130,[132][133][134][135][136] and reduced alpha power [137][138][139][140][141][142][143] in parieto-occipital areas.…”