Biology subjects

Haigh, Z. J.

Publications and source records attributed to Haigh, Z. J..

3 recordsLinked to original sources

bioRxiv2024

Abnormal mu rhythm state-related cortical and corticospinal responses in chronic stroke

The motor cortexs activity is state-dependent. Specifically, the sensorimotor mu rhythm phase relates to fluctuating levels of primary motor cortex (M1) excitability, previously demonstrated in young and healthy volunteers. However, it is unknown whether this observation is generalizable to individuals with brain lesions after a stroke. We investigated the phase relationship between the mu rhythm and cortical excitability by combining real-time processing of electroencephalography (EEG) signals and transcranial magnetic stimulation (TMS) of M1. In 11 chronic subcortical stroke survivors and 12 similar-aged healthy volunteers, we applied TMS to M1 at the peak, falling, trough, and rising phase of the sensorimotor mu oscillation. As outcome measures, we investigated the M1-to-muscle excitability by measuring motor-evoked potentials (MEPs) and local cortical activation by measuring TMS-evoked potentials (TEPs). We found that M1-to-muscle excitability in stroke survivors and older volunteers shows a phase-dependency similar to that in young healthy adults. That is, MEPs were increased and decreased at the trough and peak of the mu rhythm, respectively. However, individuals with stronger stroke-related motor symptoms showed a decreased phase preference. Further, phase-dependency was abolished in the local cortical activity, as measured with EEG, in the stroke-affected hemisphere, in contrast to the non-affected hemisphere as well as either hemisphere in healthy volunteers. Altogether, these results shed light on the state-dependency of motor cortex excitability after stroke. Our results indicate that the strength of phase preference of TMS motor responses could indicate the severity of motor impairment. These results could enable the development of improved TMS paradigms for recovery of motor impairment after stroke.

neuroscience↗

bioRxiv2023

Induced neural phase precession through exogeneous electric fields

The gradual shifting of preferred neural spiking relative to local field potentials (LFPs), known as phase precession, plays a prominent role in neural coding. Correlations between the phase precession and behavior have been observed throughout various brain regions. As such, phase precession is suggested to be a global neural mechanism that promotes local neuroplasticity. However, causal evidence and neuroplastic mechanisms of phase precession are lacking so far. Here we show a causal link between LFP dynamics and phase precession. In three experiments, we modulated LFPs in humans, a non-human primate, and computational models using alternating current stimulation. We show that continuous stimulation of motor cortex oscillations in humans lead to a gradual phase shift of maximal corticospinal excitability by [~]90{degrees}. Further, exogenous alternating current stimulation induced phase precession in a subset of entrained neurons ([~]30%) in the non-human primate. Multiscale modeling of realistic neural circuits suggests that alternating current stimulation-induced phase precession is driven by NMDA-mediated synaptic plasticity. Altogether, the three experiments provide mechanistic and causal evidence for phase precession as a global neocortical process. Alternating current-induced phase precession and consequently synaptic plasticity is crucial for the development of novel therapeutic neuromodulation methods.

neuroscience↗

bioRxiv2022

The phase of sensorimotor mu and beta oscillations has the opposite effect on corticospinal excitability

Neural oscillations in the primary motor cortex (M1) shape corticospinal excitability. Power and phase of ongoing mu (8-13 Hz) and beta (14-30 Hz) activity may mediate motor cortical output. However, the functional dynamics of both mu and beta phase and power relationships and their interaction, are largely unknown. Here, we employ recently developed real-time targeting of the mu and beta rhythm, to apply phase-specific brain stimulation and probe motor corticospinal excitability non-invasively. For this, we used instantaneous read-out and analysis of ongoing oscillations, targeting four different phases (0{degrees}, 90{degrees}, 180{degrees}, and 270{degrees}) of mu and beta rhythms with suprathreshold single-pulse transcranial magnetic stimulation (TMS) to M1. Ensuing motor evoked potentials (MEPs) in the right first dorsal interossei muscle were recorded. Twenty healthy adults took part in this double-blind randomized crossover study. Mixed model regression analyses showed significant phase-dependent modulation of corticospinal output by both mu and beta rhythm. Strikingly, these modulations exhibit a double dissociation. MEPs are larger at the mu trough and rising phase and smaller at the peak and falling phase. For the beta rhythm we found the opposite behavior. Also, mu power, but not beta power, was positively correlated with corticospinal output. Power and phase effects did not interact for either rhythm, suggesting independence between these aspects of oscillations. Our results provide insights into real-time motor cortical oscillation dynamics, which offers the opportunity to improve the effectiveness of TMS by specifically targeting different frequency bands.

neuroscience↗