Blog Archives

Distraction task rather than focal attention modulates gamma activity associated with auditory steady-state responses (ASSRs)

Conclusions
The phase-locked measures of 40Hz ASSR are attenuated when attention to the stimulation is low, i.e. the subject is effortfully focused on the competitive “distraction” task performance. Lower arousal level increases the total intensity of 40Hz ASSRs.

from Clinical Neurophysiology

Advertisements

Distraction task rather than focal attention modulates gamma activity associated with auditory steady-state responses (ASSRs)

Conclusions
The phase-locked measures of 40Hz ASSR are attenuated when attention to the stimulation is low, i.e. the subject is effortfully focused on the competitive “distraction” task performance. Lower arousal level increases the total intensity of 40Hz ASSRs.

from Clinical Neurophysiology

Temporal dynamics of sinusoidal and non-sinusoidal amplitude modulation

Previous behavioural studies in human subjects have demonstrated the importance of amplitude modulations to the process of intelligible speech perception. In functional neuroimaging studies of amplitude modulation processing, the inherent assumption is that all sounds are decomposed into simple building blocks, i.e. sinusoidal modulations. The encoding of complex and dynamic stimuli is often modelled to be the linear addition of a number of sinusoidal modulations and so, by investigating the response of the cortex to sinusoidal modulation, an experimenter can probe the same mechanisms used to encode speech. The experiment described in this paper used magnetoencephalography to measure the auditory steady-state response produced by six sounds, all modulated in amplitude at the same frequency but which formed a continuum from sinusoidal to pulsatile modulation. Analysis of the evoked response shows that the magnitude of the envelope-following response is highly non-linear, with sinusoidal amplitude modulation producing the weakest steady-state response. Conversely, the phase of the steady-state response was related to the shape of the modulation waveform, with the sinusoidal amplitude modulation producing the shortest latency relative to the other stimuli. It is shown that a point in auditory cortex produces a strong envelope following response to all stimuli on the continuum, but the timing of this response is related to the shape of the modulation waveform. The results suggest that steady-state response characteristics are determined by features of the waveform outside of the modulation domain and that the use of purely sinusoidal amplitude modulations may be misleading, especially in the context of speech encoding.

from the European Journal of Neuroscience

Fluctuation of gamma-band phase synchronization within the auditory cortex in schizophrenia

Greater intra and inter hemispheric fluctuations of ASSR gamma band phase synchronization in Sz add to previous studies suggesting timing deficiencies within neural populations, possibly caused by impairments of neural network parameters.

from Clinical Neurophysiology