The Effects of Filter's Class, Cutoff Frequencies, and Independent Component Analysis on the Amplitude of Somatosensory Evoked Potentials Recorded from Healthy Volunteers

Objective: The aim of this study was to investigate the effects of different preprocessing parameters on the amplitude of median nerve somatosensory evoked potentials (SEPs). Methods: Different combinations of two classes of filters (Finite Impulse Response (FIR) and Infinite Impulse Response (IIR)), three cutoff frequency bands (0.5–1000 Hz, 3–1000 Hz, and 30–1000 Hz), and independent component analysis (ICA) were used to preprocess SEPs recorded from 17 healthy volunteers who participated in two sessions of 1000 stimulations of the right median nerve. N30 amplitude was calculated from frontally placed electrode (F3). Results: The epochs classified as artifacts from SEPs filtered with FIR compared to those filtered with IIR were 1% more using automatic and 140% more using semi-automatic methods (both p < 0.001). There were no differences in N30 amplitudes between FIR and IIR filtered SEPs. The N30 amplitude was significantly lower for SEPs filtered with 30–1000 Hz compared to the bandpass frequencies 0.5–1000 Hz and 3–1000 Hz. The N30 amplitude was significantly reduced when SEPs were cleaned with ICA compared to the SEPs from which non-brain components were not removed using ICA. Conclusion: This study suggests that the preprocessing of SEPs should be done carefully and the neuroscience community should come to a consensus regarding SEP preprocessing guidelines, as the preprocessing parameters can affect the outcomes that may influence the interpretations of results, replicability, and comparison of different studies

Reasons for ceiling ratings in real-life evaluations of hearing aids: the relationship between SNR and hearing aid ratings

IntroductionIn past Ecological Momentary Assessment (EMA) studies, hearing aid outcome ratings have often been close to ceiling.MethodsTo analyze the underlying reasons for the very positive ratings, we conducted a study with 17 experienced hearing aid wearers who were fitted with study hearing aids. The acceptable noise level and the noise level where participants were unable to follow speech were measured. The participants then rated hearing aid satisfaction, speech understanding and listening effort for pre-defined SNRs between −10 and +20 dB SPL in the laboratory. These ratings were compared to ratings of a two-week EMA trial. Additionally, estimates of SNRs were collected from hearing aids during the EMA trial and we assessed whether the participants experienced those SNRs rated poorly in the laboratory in real life.ResultsThe results showed that for hearing aid satisfaction and speech understanding, the full rating scale was used in the laboratory, while the ratings in real life were strongly skewed towards the positive end of the scale. In the laboratory, SNRs where participants indicated they could not follow the narrator (“unable to follow” noise level) were rated clearly better than the lowest possible ratings. This indicates that very negative ratings may not be applicable in real-life testing. The lower part of the distribution of real-life SNR estimates was related to participants’ individual “unable to follow” noise levels and the SNRs which were rated poorly in the laboratory made up less than 10% of the speech situations experienced in real life.DiscussionThis indicates that people do not seem to frequently experience listening situations at SNRs where they are dissatisfied with their hearing aids and this could be the reason for the overly positive hearing aid outcome ratings in EMA studies. It remains unclear to what extent the scarcity of such situations is due lack of encounters or intentional avoidance

Chiropractic Spinal Adjustment Increases the Cortical Drive to the Lower Limb Muscle in Chronic Stroke Patients

This study aimed to investigate the effects of a single session of chiropractic spinal adjustment on the cortical drive to the lower limb in chronic stroke patients. In a single-blinded, randomized controlled parallel design study, 29 individuals with chronic stroke and motor weakness in a lower limb were randomly divided to receive either chiropractic spinal adjustment or a passive movement control intervention. Before and immediately after the intervention, transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) were recorded from the tibialis anterior (TA) muscle of the lower limb with the greatest degree of motor weakness. Differences in the averaged peak-peak MEP amplitude following interventions were calculated using a linear regression model. Chiropractic spinal adjustment elicited significantly larger MEP amplitude (pre = 0.24 ± 0.17 mV, post = 0.39 ± 0.23 mV, absolute difference = +0.15 mV, relative difference = +92%, p < 0.001) compared to the control intervention (pre = 0.15 ± 0.09 mV, post = 0.16 ± 0.09 mV). The results indicate that chiropractic spinal adjustment increases the corticomotor excitability of ankle dorsiflexor muscles in people with chronic stroke. Further research is required to investigate whether chiropractic spinal adjustment increases dorsiflexor muscle strength and walking function in people with stroke

Manipulation of dysfunctional spinal joints affects sensorimotor integration in the prefrontal cortex: a brain source localization study

Objectives. Studies have shown decreases in N30 somatosensory evoked potential (SEP) peak amplitudes following spinal manipulation (SM) of dysfunctional segments in subclinical pain (SCP) populations. This study sought to verify these findings and to investigate underlying brain sources that may be responsible for such changes. Methods. Nineteen SCP volunteers attended two experimental sessions, SM and control in random order. SEPs from 62-channel EEG cap were recorded following median nerve stimulation (1000 stimuli at 2.3 Hz) before and after either intervention. Peak-to-peak amplitude and latency analysis was completedfor different SEPs peak. Dipolar models of underlying brain sources were built by using the brain electrical source analysis. Twoway repeated measures ANOVA was used to assessed differences in N30 amplitudes, dipole locations, and dipole strengths. Results. SM decreased the N30 amplitude by 16.9 &plusmn; 31.3% (P = 0.02), while no differences were seen following the control intervention (P = 0.4). Brain source modeling revealed a 4-source model but only the prefrontal source showed reduced activity by 20.2 &plusmn; 12.2% (P = 0.03) following SM. Conclusion. A single session of spinal manipulation of dysfunctional segments in subclinical pain patients alters somatosensory processing at the cortical level, particularly within the prefrontal cortex