Gamma oscillation plasticity is mediated via parvalbumin interneurons

Rodent and human seizures demonstrate a dynamic interplay with spreading depolarizations

Seizure termination has been linked to spreading depolarizations (SDs) in experimental models of epilepsy, and SDs have been suggested to protect against seizures. However, the precise mechanisms of seizure-associated SDs remain unclear. Additionally, the co-occurrence of SDs with human seizures remains debated. In this study, we found that SDs are a prominent feature following ictal events in both human clinical recordings and in a rodent model of ictogenesis. Approximately one-third of rodent seizure-like events (SLEs) associated with SDs, while all human seizures analyzed associated with propagating infraslow shifts, indicative of SDs. In rodents, SDs clustered towards the end of ictal events, resulting in significantly shorter SLEs and delayed onset of subsequent SLEs. Interestingly, SLEs with SDs displayed significantly more low gamma activity during ictal events than SLEs that did not end in SDs. Furthermore, we found no significant correlation between [K+]o levels and the likelihood of SLEs ending in SDs, questioning the role of [K+]o in SD induction during seizures. Interestingly, the human data demonstrate clear SD propagation during seizures and show that SDs appear and propagate in multiple brain regions simultaneously with ictal events. Collectively, these results indicate that SDs are a hallmark of ictal activity associated with seizure termination. Furthermore, these findings provide unique insight into the neuronal dynamics that promote SD induction by showing that increased low gamma activity during SLEs is more predictive of SD induction than [K+]o levels. Taken together, these findings provide rationale for further exploration of SDs to prematurely terminate life-threatening seizures.

Perineuronal net degradation causes a delayed change in resting and sound evoked responses in the mouse auditory cortex

Perineuronal nets (PNNs) are extracellular matrix assemblies that preferentially cover parvalbumin-expressing (PV+) interneurons in the neocortex. PV+ cells and PNNs are impaired in a variety of neurodevelopmental disorders including Fragile X Syndrome and schizophrenia. In both of these disorders, electroencephalograph (EEG) recordings show similar phenotypes, including elevated resting gamma band power and reduced temporal fidelity in the 40 Hz auditory steady state response (ASSR). Whether there is a causal link between PNN integrity and EEG abnormalities remains unclear. We tested this link by recording EEG responses in the auditory cortex (AC) in wildtype mice in which PNNs were enzymatically degraded (Chondroitinase ABC or ChABC). EEGs were recorded at two different time points (4- or 14-days post injection, cross-sectional design). In comparison to saline control, ChABC injected mice showed a ∼50 % reduction in PNN density after 4-days. However, there was no difference in resting EEG power spectral density, auditory event-related potential amplitudes or ASSR temporal fidelity between saline and ChABC mice. At the 14-day time point, there was a recovery of PNN density in the AC. Interestingly, EEG responses were abnormal at this time point, with elevated gamma band activity and reduced ASSR temporal fidelity. Thus, the electrophysiological consequences of PNN loss are not seen acutely, but over a delayed time course, suggesting abnormal plasticity after a circuit perturbation. Taken together, these data indicate acute shaping of auditory cortical responses is less dependent on PNNs, but long-term stability of responses following a circuit perturbation depends on the integrity of PNNs.

A Role for δ Subunit-Containing GABAA Receptors on Parvalbumin-Positive Neurons in Maintaining Electrocortical Signatures of Sleep States

GABAA receptors containing δ subunits have been shown to mediate tonic/slow inhibition in the CNS. These receptors are typically found extrasynaptically and are activated by relatively low levels of ambient GABA in the extracellular space. In the mouse neocortex, δ subunits are expressed by some pyramidal cells as well as on parvalbumin-positive (PV+) interneurons. An important function of PV+ interneurons is the organization of coordinated network activity that can be measured by EEG. However, it remains unclear what role tonic/slow inhibitory control of PV+ neurons may play in shaping oscillatory activity. After validating expected functional loss of δ-associated current in cortex of PV δcKO mice of both sexes, we performed EEG recordings to survey network activity across wake and sleep states. PV δcKO mice showed altered spectral content of EEG during NREM and REM sleep that was a result of increased oscillatory activity in NREM and the emergence of transient high-amplitude bursts of theta-frequency activity during REM. Viral reintroduction of Gabrd to PV+ interneurons in PV δcKO mice rescued REM EEG phenotypes, supporting an important role for δ subunit-mediated inhibition of PV+ interneurons for maintaining normal REM cortical oscillations.

The relationship between neuromagnetic networks and cognitive impairment in self-limited epilepsy with centrotemporal spikes

OBJECTIVE

This was an exploratory study designed to examine the alterations in neuromagnetic networks within brain regions involved in cognitive functions in children with self-limited epilepsy with centrotemporal spikes (SeLECTS). Additionally, it sought to explore the relationship between these neural network differences and cognitive impairment.

METHODS

Magnetoencephalography (MEG) data were collected from 63 drug-naïve children diagnosed with SeLECTS and 30 healthy controls (HC). Functional connectivity (FC) across 26 cognitive-related brain regions, as defined by Desikan-Killiany, was assessed using corrected amplitude envelope correlation (AEC-c) analysis. The cognitive function of the children was evaluated using the fourth edition of the Wechsler Intelligence Scale for Children (WISC-IV). Spearman's correlation analysis was then performed to assess the relationship between AEC-c values and WISC-IV indices.

RESULTS

Children with SeLECTS showed reduced FC in the delta band between the left rostral middle frontal (rMFG.L) and the left rostral anterior cingulate (rACC.L), as well as in the gamma2 band between the left superior frontal (SFG.L) and the rACC on both sides, compared to HC (p < 0.05). On the other hand, several FC networks were enhanced, including those between the left rMFG and the right rACC, the left rMFG and the left caudal middle frontal (CMF.L), and between the right caudal middle frontal (CMF.R) and the right supramarginal (SMG.R), specifically in the gamma1 band (p < 0.05). A correlation analysis revealed a positive association between the AEC-c values between the left rMFG and the right rACC and the Verbal Comprehension Index (VCI) scores (R = 0.4228, p < 0.05).

SIGNIFICANCE

The findings of this study revealed that children with SeLECTS exhibited significant differences in the FC networks in brain regions associated with cognition, especially within the delta and gamma frequency bands, when compared to HC. We also found that these differences in FC networks are significantly correlated with verbal comprehension ability, which may contribute to the understanding of the mechanisms underlying the weaknesses in cognitive function in children with SeLECTS. Furthermore, our findings may provide hypotheses for future work dedicated to further exploring the mechanisms associated with brain network alterations in cognitive impairment in children with SeLECTS.

PLAIN LANGUAGE SUMMARY

Based on magnetoencephalography technology (MEG), this study found that there were significant differences in cognitive-related neuromagnetic networks in children with SeLECTS compared with HC, which were significantly correlated with relevant indicators in the Wechsler Scale. This finding suggested that differences in the neuromagnetic network may serve as imaging markers to predict changes in cognitive function in children with SeLECTS.

Parvalbumin interneurons regulate rehabilitation-induced functional recovery after stroke and identify a rehabilitation drug

Motor disability is a critical impairment in stroke patients. Rehabilitation has a limited effect on recovery; but there is no medical therapy for post-stroke recovery. The biological mechanisms of rehabilitation in the brain remain unknown. Here, using a photothrombotic stroke model in male mice, we demonstrate that rehabilitation after stroke selectively enhances synapse formation in presynaptic parvalbumin interneurons and postsynaptic neurons in the rostral forelimb motor area with axonal projections to the caudal forelimb motor area where stroke was induced (stroke-projecting neuron). Rehabilitation improves motor performance and neuronal functional connectivity, while inhibition of stroke-projecting neurons diminishes motor recovery. Stroke-projecting neurons show decreased dendritic spine density, reduced external synaptic inputs, and a lower proportion of parvalbumin synapse in the total GABAergic input. Parvalbumin interneurons regulate neuronal functional connectivity, and their activation during training is necessary for recovery. Furthermore, gamma oscillation, a parvalbumin-regulated rhythm, is increased with rehabilitation-induced recovery in animals after stroke and stroke patients. Pharmacological enhancement of parvalbumin interneuron function improves motor recovery after stroke, reproducing rehabilitation recovery. These findings identify brain circuits that mediate rehabilitation-recovery and the possibility for rational selection of pharmacological agents to deliver the first molecular-rehabilitation therapeutic.

Advancing personalized digital therapeutics: integrating music therapy, brainwave entrainment methods, and AI-driven biofeedback

Mental health disorders and cognitive decline are pressing global concerns, increasing the demand for non-pharmacological interventions targeting emotional dysregulation, memory deficits, and neural dysfunction. This review systematically examines three promising methodologies-music therapy, brainwave entrainment (binaural beats, isochronic tones, multisensory stimulation), and their integration into a unified therapeutic paradigm. Emerging evidence indicates that music therapy modulates affect, reduces stress, and enhances cognition by engaging limbic, prefrontal, and reward circuits. Brainwave entrainment, particularly within the gamma frequency range (30-100 Hz), facilitates neural oscillatory patterns linked to relaxation, concentration, and memory, with 40 Hz showing promise for cognitive enhancement, albeit with individual variability. Synchronized multisensory stimulation, combining auditory and visual inputs at gamma frequencies, has demonstrated potential in enhancing memory and supporting neural integrity, particularly in Alzheimer's disease. However, challenges such as patient response variability, lack of standardization, and scalability hinder widespread implementation. Recent research suggests that a synergistic application of these modalities may optimize therapeutic outcomes by leveraging complementary mechanisms. To actualize this, AI-driven biofeedback, enabling real-time physiological assessment and individualized adjustments-such as tailoring musical complexity, entrainment frequencies, and multisensory components-emerges as a promising solution. This adaptive model enhances treatment accessibility and consistency while maximizing long-term efficacy. Although in early stages, preliminary evidence highlights its transformative potential in reshaping non-pharmacological therapeutic strategies. Advancing this field requires interdisciplinary research, rigorous evaluation, and ethical data stewardship to develop innovative, patient-centered solutions for mental health and cognitive rehabilitation.

The Excessive Tonic Inhibition of the Peri-infarct Cortex Depresses Low Gamma Rhythm Power During Poststroke Recovery

The cortex immediately surrounding a brain ischemic lesion, the peri-infarct cortex (PIC), harbors a large part of the potential to recover lost functions. However, our understanding of the neurophysiological conditions in which synaptic plasticity operates remains limited. Here we hypothesized that the chronic imbalance between excitation and inhibition of the PIC prevents the normalization of the gamma rhythm, a waveband of neural oscillations thought to orchestrate action potential trafficking. Probing the local field potential activity of the forelimb primary sensory cortex (S1FL) located in the PIC of male adult mice, we found a constant, deep reduction of low-gamma oscillation power (L-gamma; 30-50 Hz) precisely during the critical time window for recovery (1-3 weeks after stroke). The collapse of L-gamma power negatively correlated with behavioral progress in affected forelimb use. Mapping astrocyte reactivity and GABA-like immunoreactivity in the PIC revealed a parallel high signal, which gradually increased when approaching the lesion. Increasing tonic inhibition with local infusion of GABA or by blocking its recapture reduced L-gamma oscillation power in a magnitude similar to stroke. Conversely, the negative allosteric modulation of tonic GABA conductance using L655,708 or the gliopeptide ODN rescued the L-gamma power of the PIC. Altogether the present data point out that the chronic excess of ambient GABA in the PIC limits the generation of L-gamma oscillations in the repairing cortex and suggests that rehabilitative interventions aimed at normalizing low-gamma power within the critical period of stroke recovery could optimize the restitution of lost functions.

Defects of parvalbumin-positive interneurons are implicated in psychiatric disorders

Psychiatric disorders are a common cause of severe long-term disability and socioeconomic burden worldwide. Although our understanding of these disorders has advanced substantially over the last few years, little has changed the standards of care for these illnesses. Fast-spiking parvalbumin-positive interneurons (PVIs), a subpopulation of gamma-aminobutyric acid (GABA)ergic interneurons, are widely distributed in the hippocampus and have been reported to play an important role in various mental disorders. However, the mechanisms underlying the regulation of the molecular networks relevant to depression and schizophrenia (SCZ) are unknown. Here, we discuss the functions of PVIs in psychiatric disorders, including depression and SCZ. After reviewing several studies, we concluded that dysfunction in PVIs could cause depression-like behavior, as well as cognitive categories in SCZ, which might be mediated in large part by greater synaptic variability. In summary, this scientific review aims to discuss the current knowledge regarding the function of PVIs in depression and SCZ. Moreover, we highlight the importance of neurogenesis and synaptic plasticity in the pathogenesis of depression and SCZ, which seem to be mediated by PVIs activity. These findings provide a better understanding of the role of PVIs in psychiatric disorders.

The Role of Parvalbumin Interneurons in Autism Spectrum Disorder

As an important subtype of GABAergic interneurons, parvalbumin (PV) interneurons play a critical role in regulating cortical circuits and neural networks. Abnormalities in the development or function of PV interneurons have been linked to autism spectrum disorder (ASD), a neurodevelopmental disorder characterized by social and language deficits. In this review, we focus on the abnormalities of PV interneurons in ASD, including quantity and function and discuss the underlying mechanisms of impairments in PV interneurons in the pathology of ASD. Finally, we propose potential therapeutic approaches targeting PV interneurons, such as transplanting MGE progenitor cells and utilizing optogenetic stimulation in the treatment of ASD.

Parvalbumin interneuron cell-to-network plasticity: mechanisms and therapeutic avenues

Alzheimer's disease (AD) and schizophrenia (SCZ) represent two major neuropathological conditions with a high disease burden. Despite their distinct etiologies, patients suffering from AD or SCZ share a common burden of disrupted memory functions unattended by current therapies. Recent preclinical analyses highlight cell-type-specific contributions of parvalbumin interneurons (PVIs), particularly the plasticity of their cellular excitability, towards intact neuronal network function (cell-to-network plasticity) and memory performance. Here we argue that deficits of PVI cell-to-network plasticity may underlie memory deficits in AD and SCZ, and we explore two therapeutic avenues: the targeting of PVI-specific neuromodulation, including by neuropeptides, and the recruitment of network synchrony in the gamma frequency range (40 Hz) by external stimulation. We finally propose that these approaches be merged under consideration of recent insights into human brain physiology.

Mechanisms and implications of gamma oscillation plasticity

A recent study by Hadler and colleagues uncovered a novel form of plasticity of gamma oscillations in an ex vivo hippocampal slice preparation which they term 'gamma potentiation'. We discuss the potential cellular mechanisms of this form of plasticity and its functional and translational implications.

A role for δ subunit-containing GABA A receptors on parvalbumin positive neurons in maintaining electrocortical signatures of sleep states

GABA A receptors containing δ subunits have been shown to mediate tonic/slow inhibition in the CNS. These receptors are typically found extrasynaptically and are activated by relatively low levels of ambient GABA in the extracellular space. In the mouse neocortex, δ subunits are expressed on the surface of some pyramidal cells as well as on parvalbumin positive (PV+) interneurons. An important function of PV+ interneurons is the organization of coordinated network activity that can be measured by EEG; however, it remains unclear what role tonic/slow inhibitory control of PV+ neurons may play in shaping oscillatory activity. After confirming a loss of functional δ mediated tonic currents in PV cells in cortical slices from mice lacking Gabrd in PV+ neurons (PV δcKO), we performed EEG recordings to survey network activity across wake and sleep states. PV δcKO mice showed altered spectral content of EEG during NREM and REM sleep that was a result of increased oscillatory activity in NREM and the emergence of transient high amplitude bursts of theta frequency activity during REM. Viral reintroduction of Gabrd to PV+ interneurons in PV δcKO mice rescued REM EEG phenotypes, supporting an important role for δ subunit mediated inhibition of PV+ interneurons for maintaining normal REM cortical oscillations.

Significance statement

The impact on cortical EEG of inhibition on PV+ neurons was studied by deleting a GABA A receptor subunit selectively from these neurons. We discovered unexpected changes at low frequencies during sleep that were rescued by viral reintroduction.