Impact of interhemispheric inhibition on bimanual movement control in young and old

Interhemispheric interactions demonstrate a crucial role for directing bimanual movement control. In humans, a well-established paired-pulse transcranial magnetic stimulation paradigm enables to assess these interactions by means of interhemispheric inhibition (IHI). Previous studies have examined changes in IHI from the active to the resting primary motor cortex during unilateral muscle contractions; however, behavioral relevance of such changes is still inconclusive. In the present study, we evaluated two bimanual tasks, i.e., mirror activity and bimanual anti-phase tapping, to examine behavioral relevance of IHI for bimanual movement control within this behavioral framework. Two age groups (young and older) were evaluated as bimanual movement control demonstrates evident behavioral decline in older adults. Two types of IHI with differential underlying mechanisms were measured; IHI was tested at rest and during a motor task from the active to the resting primary motor cortex. Results demonstrate an association between behavior and short-latency IHI in the young group: larger short-latency IHI correlated with better bimanual movement control (i.e., less mirror activity and better bimanual anti-phase tapping). These results support the view that short-latency IHI represents a neurophysiological marker for the ability to suppress activity of the contralateral side, likely contributing to efficient bimanual movement control. This association was not observed in the older group, suggesting age-related functional changes of IHI. To determine underlying mechanisms of impaired bimanual movement control due to neurological disorders, it is crucial to have an in-depth understanding of age-related mechanisms to disentangle disorder-related mechanisms of impaired bimanual movement control from age-related ones.

Improving methods for diagnosing occupational hearing loss

Introduction. Since the share of sensorineural hearing loss in the structure of occupational morbidity in the Russian Federation increased by 1.5 times in 2018 compared to 2007, it is essential to ensure the reliability of the results of diagnostic studies to establish the fact of hearing impairment as a result of occupational noise. Materials and methods. Retrospectively for the period 2008-2017 the analysis of the prevalence and dynamics of occupational hearing loss in the Republic of Bashkortostan (RB) was carried out. Objectification of the state of the auditory sensory analyzer was carried out in 30 patients with occupational hearing loss using tonal threshold audiometry and registration of short-latency auditory evoked potentials. Results. In the RB, the number of occupational diseases caused by exposure to physical factors has doubled, mainly due to occupational hearing loss with a mild course of the process. The obtained indicators of short-latency auditory evoked potentials determined the difference in the latencies of the recorded potentials, amplitudes and intervals in persons with impaired auditory function of professional origin and in a group of persons from the control group who did not have industrial acoustic contact. Conclusion. The increase in the number of patients with occupational hearing loss requires the development of measures for their timely and objective diagnosis and medical care. The method of recording short-latency auditory evoked potentials is sensitive and quite informative in diagnosing hearing loss from exposure to occupational noise.

Neurophysiological Predictors of Response to Medication in Parkinson's Disease

Background: Although dopaminergic medication has been the foundation of Parkinson's disease (PD) therapy for decades, sensitive and specific therapeutic response biomarkers that allow for better treatment optimization are lacking.Objective: We tested whether the features of Transcranial Magnetic Stimulation-based neurophysiological measures taken off-medication are associated with dopaminergic medication-induced clinical effects.Method: Motor cortex excitability [short-latency intracortical inhibition (SICI), intracortical facilitation (ICF), short-latency afferent inhibition (SAI), and input-output (IO) curve], and plasticity [paired associative stimulation (PAS) protocol] neurophysiological measures were examined in 23 PD patients off-medication. Clinical features were quantified by the motor section of the Unified Parkinson's Disease Scale (total score and lateralized total, bradykinesia, and rigidity sub-scores), and the differences between measures off-medication and on-medication (following the usual morning dose), were determined. Total daily dopaminergic medication dose (expressed as levodopa equivalent daily dose-LEDD), was also determined.Results: SICI significantly correlated with changes in lateralized UPDRS motor and bradykinesia sub-scores, suggesting that patients with stronger basal intracortical inhibition benefit more from dopaminergic treatment than patients with weaker intracortical inhibition. Also, ICF significantly negatively correlated with LEDD, suggesting that patients with stronger intracortical facilitation require less dopaminergic medication to achieve optimal therapeutic benefit. Both associations were independent of disease severity and duration.Conclusions: The results suggest variability of (patho) physiological phenotypes related to intracortical inhibitory and facilitatory mechanisms determining clinical response to dopaminergic medication in PD. Measures of intracortical excitability may help predict patients' response to dopaminergic therapy, thus potentially providing a background for developing personalized therapy in PD.

Amplitude of Somatosensory Evoked Potentials (SEPs) in Short-Latency SEPs Condition is 80% of that in Giant SEPs

The recording conditions of somatosensory evoked potentials (giant SEPs) are different from those of short-latency SEPs (SSEPs). We investigated the waveform characteristics obtained for each condition. Forty-eight upper limbs of 24 adult normal subjects (12 males, age 35.5 ± 9.7 years (mean ± SD)) were investigated. The main differences in recording conditions were reference electrodes (giant SEPs: the earlobe electrode ipsilateral to the stimulated limb, SSEPs: Fz), stimulus rate (1 Hz, 5 Hz), and bandpass filter (1 Hz–1 kHz, 20 Hz–3 kHz). SEPs were elicited by unilateral percutaneous electrical stimulation of the median nerve at the wrist. The amplitudes of N20o–N20 and N20–P25 were significantly larger in the giant SEP condition than in the SSEP condition (p<0.001). The mean + 3SD of N20–P25 amplitude was 10.0 µV in the giant SEP condition and 7.8 µV in the SSEP condition. The N20–P25 amplitude was significantly correlated between the giant SEP and SSEP conditions (R=0.64, p<0.001). Thus, the amplitude of SEPs in the SSEPs condition is equivalent to 80% of that in the giant SEPs condition. The information is useful for detecting cortical hyperexcitability in various neurological disorders including myoclonic epilepsy.

Inhibitory interactions in the system of functionally connected muscles of the shin in patients with the cerebral palsy

In 10 able-bodied individuals and 8 patients with the cerebral palsy reciprocal and non-reciprocal inhibitions of soleus motoneurones were investigated by means of the H-reflex conditioned by electrical stimulation of the tibialis and gastrocnemius medialis nerves, respectively. In normal individuals short- and long-latency periods of both reciprocal and non-reciprocal inhibitions were found. The cerebral palsy patients showed the increased inhibitory influence with more enhanced short-latency components of inhibition. A possible role of inhibitory systems in limitation of patologically activated antigravitant soleus motoneurones was discussed.

Transient peripheral vestibular hypofunction measured with vestibular short-latency evoked potentials following noise exposure in rats

Exposure to 120 decibel sound pressure level (dB SPL) band-limited noise results in delayed onset latency and reduced vestibular short-latency evoked potential (VsEP) responses. These changes are still present four weeks after noise overstimulation. Noise induced hearing loss (NIHL) has been shown to vary in extent and duration based on noise intensity. This study investigated whether noise-induced peripheral vestibular hypofunction (NPVH) would also decrease in extent and/or duration with less intense noise exposure. In the present study, rats were exposed to a less intense noise (110dB SPL), but for the same duration (6 hours) and frequency range (500-4000 Hz) as used in previous studies. The VsEP was assessed 1, 3, 7, 14, 21, and 28 days after noise exposure. In contrast to 120 dB SPL noise exposure, the 110 dB SPL noise exposures produced smaller deficits in VsEP responses that fully recovered in 62% of animals (13/21) within one week. These findings suggest that NPVH, a loss or attenuation of VsEP responses with a requirement for elevated stimulus intensity to elicit measurable responses, is similar to NIHL, i.e., lower sound levels produce a smaller or transient deficit. These results show it will be important to determine the extent and duration of vestibular hypofunction for different noise exposure conditions and their impact on balance.