Modulation of motor cortical excitability with auditory stimulation

Loud sounds have been demonstrated to increase motor cortex excitability when transcranial magnetic stimulation (TMS) is synchronized with auditory evoked N100 potential measured from electroencephalography (EEG). The N100 potential is generated by an afferent response to sound onset and feature analysis, and upon novel sound it is also related to the arousal reaction. The arousal reaction is known to originate from the ascending reticular activating system of the brain stem and to modulate neuronal activity throughout the central nervous system. In this study we investigated the difference in motor evoked potentials (MEPs) when deviant and novelty stimuli were randomly interspersed in a train of standard tones. Twelve healthy subjects participated in this study. Three types of sound stimuli were used: 1) standard stimuli (800 Hz), 2) deviant stimuli (560 Hz), and 3) novelty stimuli (12 different sounds). In each stimulus sequence 600 stimuli were given. Of these, 90 were deviant stimuli randomly placed between the standard stimuli. Each of 12 novel sounds was presented once in pseudorandomized order. TMS was randomly mixed with the sound stimuli so that it was either synchronized with the individual N100 or trailed the sound onset by 200 ms. All sounds elicited an increase in motor cortex excitability. The type of sound had no significant effect. We also demonstrated that TMS timed at 200-ms intervals caused a significant increment of MEPs. This contradicted our hypothesis that MEP amplitudes to TMS synchronized with N100 would be greater than those to TMS at 200 ms after a sound and remains unexplained. NEW & NOTEWORTHY We demonstrated modulation of motor cortical excitability with parallel auditory stimulus by combining navigated transcranial magnetic stimulation (TMS) with auditory stimuli. TMS was synchronized with auditory evoked potentials considered to be generated by the unconscious attention call process in the auditory system.

Ascending Reticular Activating System of the Brain

There were two stages in the history of the studies on ascending reticular activating system of the brain (ARAS). The first stage began with the ARAS discovery by Magoun and Moruzzi and the following investigations using the methods of stimulation and lesion at that time mainly in acute cats. These studies led to the hypothesis of a “diffuse” and “unspecific” ARAS of the brain stem. The second stage was associated with using more precise neurophysiological and histochemical methods mainly in chronically operated free-moving cats and rats. By 2010, the idea of the ARAS as an organized hierarchy of the cerebral “waking centers” distributed along the entire cerebral axis and releasing all the known neuromediators of low molecular weight together with the most important neuropeptides was formulated. To date, the aforementioned hypothesis has been revised again. The glutamatergic activating system has been discovered and described in detail. Presumably, this system is responsible for the appearance of electroencephalogram (EEG) arousal reaction and maintenance of the neocortex in the state of tonic depolarization during wakefulness and rapid eye movement (REM) sleep. Its destruction results in a deep comatose-like state. At the same time, the activity of all other “waking centers” is probably the result of the cortical activation.

Frontal cortex reactivity differentiates between schizophrenic subtypes: auditory ERP-evidence

SUMMARYObjectives: To extend the hypothesis that late auditory EP shifts represent pathophysiologcial markers in schizophrenia. Methods: Early negative (±100 μs) and late positive (>300 ms) auditory oddball and CNV responses are topographically compared in 3 medicated schizophrenic subtypes.Results: Only late cortical responses differentiate between paranoid, residual and disorganised schizophrenia. Core features of the deficit residual state encompass low-voltage N2P3 responses and missing central initial CNV components. Both paranoid and disorganised schizophrenics show a distinctive reactivity of the frontal cortex. Paranoid schizophrenia is characterized by an extensive frontal spread of the task-related P3 response. Disorganised schizophrenia shows a specifically increased frontal CNV component indicating a nonspecific arousal reaction.Conclusion: Combinations of late auditory EP-patterns fairly fit with the cognitive/behavioral status observed in schizophrenia spectrum disorders.