Biology subjects

Semmler, J.

Publications and source records attributed to Semmler, J..

4 recordsLinked to original sources

bioRxiv2023

Modulation of dorsal premotor cortex disrupts neuroplasticity of primary motor cortex in young and older adults

Although transcranial magnetic stimulation (TMS) research demonstrates that dorsal premotor cortex (PMd) influences neuroplasticity within primary motor cortex (M1), it is unclear how ageing modifies this communication. The present study investigated the influence of PMd on different indirect (I) wave inputs within M1 that mediate cortical plasticity in young and older adults. 15 young and 15 older participants completed two experimental sessions that examined the effects of intermittent theta burst stimulation (iTBS) to M1 when preceded by iTBS (PMd iTBS-M1 iTBS) or sham stimulation (PMd sham-M1 iTBS) to PMd. Changes in corticospinal excitability post-intervention were assessed with motor evoked potentials (MEP) recorded from right first dorsal interosseous using posterior-anterior (PA) and anterior-posterior (AP) current single-pulse TMS (PA1mV; AP1mV; PA0.5mV, early I-wave; AP0.5mV, late I-wave). Although PA1mV did not change post-intervention (P = 0.628), PMd iTBS-M1 iTBS disrupted the expected facilitation of AP1mV (to M1 iTBS) in young and older adults (P = 0.002). Similarly, PMd iTBS-M1 iTBS disrupted PA0.5mV facilitation in young and older adults (P = 0.030), whereas AP0.5mV facilitation was not affected in either group (P = 0.218). This suggests that while PMd specifically influences the plasticity of early I-wave circuits, this communication is preserved in older adults.

neuroscience↗

bioRxiv2022

Modulation of I-wave generating pathways with repetitive paired-pulse transcranial magnetic stimulation: A TMS-EEG study

ObjectivesRepetitive paired-pulse transcranial magnetic stimulation (iTMS) at indirect (I) wave intervals increases motor-evoked potentials (MEPs) produced by TMS to primary motor cortex (M1). However, the effects of iTMS at early and late intervals on the plasticity of specific I-wave circuits remains unclear. The current study therefore aimed to assess how the timing of iTMS influences intracortical excitability within early and late I-wave circuits. To investigate the cortical effects of iTMS more directly, changes due to the intervention were also assessed using combined TMS-electroencephalography (EEG). Material and MethodsEighteen young adults (24.6 {+/-} 4.2 years) participated in four sessions in which iTMS targeting early (1.5 ms interval; iTMS1.5) or late (4.0 ms interval; iTMS4.0) I-waves was applied over M1. Neuroplasticity was assessed using both posterior-to-anterior (PA) and anterior-to-posterior (AP) stimulus directions to record MEPs and TEPs before and after iTMS. SICF at inter-stimulus intervals of 1.5 and 4.0 ms was also used to index I-wave activity. ResultsMEP amplitude was increased after iTMS (P < 0.01) and this was greater for PA responses (P < 0.01), but not different between iTMS intervals (P = 0.9). Irrespective of iTMS interval and coil current, SICF was facilitated after the intervention (P < 0.01). While the N45 produced by AP stimulation was reduced by iTMS1.5 (P = 0.04), no other changes in TEP amplitude were observed. ConclusionThe timing of iTMS failed to influence which I-wave circuits were potentiated by the intervention. In contrast, reductions in the N45 suggest that the neuroplastic effects of iTMS may include disinhibition of intracortical inhibitory processes.

neuroscience↗

bioRxiv2022

Utilising TMS-EEG to assess the response to cerebellar-brain inhibition

BackgroundCerebellar-brain inhibition (CBI) is a transcranial magnetic stimulation (TMS) paradigm indexing excitability of cerebellar projections to motor cortex (M1). Stimulation involved with CBI is often considered to be uncomfortable, and alternative ways to index connectivity between cerebellum and the cortex would be valuable. Utilising electroencephalography in conjunction with TMS (combined TMS-EEG) to record the response to CBI has the potential to achieve this, but has not been attempted previously. ObjectiveTo investigate the utility of TMS-EEG for characterising cerebellar-cortical interactions recruited by CBI. MethodsA total of 33 volunteers (25.7 {+/-} 4.9 years, 20 females) participated across three experiments. These investigated EEG responses to CBI induced with a figure-of-eight (F8; experiment 1) or double cone (DC; experiment 2) conditioning coil over cerebellum, in addition to multisensory sham stimulation (experiment 3). ResultsBoth F8 and DC coils suppressed early TMS-evoked EEG potentials (TEPs) produced by TMS to M1 (P < 0.05). Furthermore, the TEP produced by CBI stimulation was related to the motor inhibitory response to CBI recorded in a hand muscle (P < 0.05), but only when using the DC coil. Multisensory sham stimulation failed to modify the M1 TEP. ConclusionsCerebellar conditioning produced changes in the M1 TEP that were not apparent following sham stimulation, and that were related to the motor inhibitory effects of CBI. Our findings therefore suggest it is possible to index the response to CBI using TMS-EEG. In addition, while both F8 and DC coils appear to recruit cerebellar projections, the nature of these may be different.

neuroscience↗

bioRxiv2021

Age differences in aperiodic neural activity measured with resting EEG

Previous research using electroencephalography (EEG) and magnetoencephalography (MEG) has shown that neural oscillatory activity within the alpha band (8-12 Hz) becomes slower and lower in amplitude with advanced age. However, most studies have focused on quantifying age-related differences in periodic oscillatory activity with little consideration of the influence of aperiodic activity on these measures. The aim of this study was to investigate age differences in aperiodic activity inherent in the resting EEG signal. We assessed aperiodic activity in 85 healthy younger adults (mean age: 22.2 years, SD: 3.9, age range: 18-35, 37 male) and 92 healthy older adults (mean age: 66.1 years, SD: 8.2, age range 50-86, 53 male) by fitting the 1/f-like background activity evident in EEG power spectra using the fitting oscillations & one over f (FOOOF) toolbox. Across the scalp, the aperiodic exponent and offset were smaller in older compared to younger participants, reflecting a flatter 1/f-like slope and a downward broadband shift in the power spectra with age. Before correcting for aperiodic activity, older adults showed slower peak alpha frequency and reduced peak alpha power relative to younger adults. After correcting for aperiodic activity, peak alpha frequency remained slower in older adults; however, peak alpha power no longer differed statistically between age groups. The large sample size utilized in this study, as well as the depth of analysis, provides further evidence that the aperiodic component of the resting EEG signal is altered with aging and should be considered when investigating neural oscillatory activity.

neuroscience↗