Disruption of gamma–delta relationship related to working memory deficits in first-episode psychosis

Abstract

Working memory (WM) deficits constitute a core symptom of schizophrenia. Inadequacy of WM maintenance in schizo-phrenia has been reported to reflect abnormalities in the excitation/inhibition (E/I) balance between pyramidal neurons and parvalbumin basket cells, which may explain alterations of the dynamics of gamma and delta oscillations. To address this issue, we assessed event-related gamma (35-45 Hz) and delta (0.5-4 Hz) oscillatory responses in a visual n-back WM task in patients with first-episode psychosis (FEP) and healthy controls (HC). Periodicity analyses of oscillations were computed to explore the relationship between the psychiatric status and the WM load-related processes reflected by each frequency range. The correspondence between nested delta-gamma oscillations was estimated to assess the strength of the frontal E/I balance. In HC, gamma oscillations were synchronized by the stimulus in a 50-150 ms time range for all tasks, and periodicity of the delta cycle was comparable between the tasks. In addition, synchronization of gamma oscillations in HC occurred at the maximal descending phase of the delta cycle half-period, supporting the coexistence of delta-nested gamma oscillations. Compared with controls, FEP patients showed a lack of gamma synchronization independently of the nature of the task, and the period of delta oscillation increased significantly with the difficulty of the WM task. We thus demonstrated in FEP an inability to encode multiple items in short-term memory associated with abnormalities in the relationship between oscillations related to the difficulty of the WM task. These results argue in favor of a dysfunction of the E/I balance in psychosis.

EEG-Based Measures in At-Risk Mental State and Early Stages of Schizophrenia: A Systematic Review

“…In one study, FES subjects, as compared to HCs, had a decrease in the occurrence of anterior–to-posterior propagation of delta waves during auditory and visual tasks ( 82 ). A second study, carried out in FEP subjects, demonstrated a workload-dependent increase of the duration of delta oscillations during a working memory task ( 81 ) not observed in HCs. This was revealed by longer delta oscillation cycles in FEP during the performance of tasks of increasing difficulty.…”

“…Three studies investigated delta activity while subjects performed a task ( 81 – 83 ). In one study, FES subjects, as compared to HCs, had a decrease in the occurrence of anterior–to-posterior propagation of delta waves during auditory and visual tasks ( 82 ).…”

“…During sensory stimulation or the performance of a task, different results have been reported. In particular, several studies reported abnormalities in the evoked responses (mainly decrease in evoked gamma), synchronization (reduction or a delay in the synchronization) and connectivity (generally a reduction in functional connectivity) of gamma activity during the performance of memory ( 81 , 114 ), cognitive control ( 115 ), emotion processing ( 116 , 117 ), or auditory tasks ( 118 – 122 ) both in FES ( 114 , 115 , 117 – 122 ) and FEP ( 81 , 116 ) subjects, as compared to HCs. Furthermore, alterations in gamma synchrony were also related to social cognition in one study ( 117 ), while another one, employing a longitudinal design, highlighted that the improvement in positive symptoms in FES subjects was related to the increase in gamma synchrony ( 121 ).…”

Special Report on the Impact of the COVID-19 Pandemic on Clinical EEG and Research and Consensus Recommendations for the Safe Use of EEG

“…10,[21][22][23][24][25][26] Similarly, research also shows that qEEGderived frequency bands, microstate analysis, and event-related oscillations (EROs; non-phase locked rhythmic pattern of neural activity) are highly modified in pathological brains. [27][28][29][30] Despite encouraging data, the relevance of such tools in daily psychiatric clinics is still under investigation. Second, at a therapeutic level, it is worth noting that noninvasive brain stimulation (NIBS) that utilizes neuroelectric principles to modulate brain activity (such as transcranial direct current stimulation [tDCS], transcranial alternating current stimulation [tACS], or transcranial magnetic stimulation [TMS]) have been successfully established for the treatment of a wide range of psychiatric disorders (for a review, see Lefaucheur et al 31 ).…”

“…• EROs: The study of EROs enables the measurement of frequency-specific brain electrical oscillations in neural circuits that are related to the sensory and cognitive processing of stimuli. 88 EROs are commonly classified according to the "natural frequencies" of the brain, 89 that is, delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and gamma (30-70 Hz). The analysis of EROs yields several measures such as event-related power, event-related phase locking (intertrial coherence), event-related coherence, and cross-frequency coupling.…”