Biomedical subjects

Gary C Galbraith

Publications and source records attributed to Gary C Galbraith.

3 recordsLinked to original sources

PubMed2004

Correlated brain stem and cortical evoked responses to auditory tone change.

Numerous human studies have separately observed the effects of auditory stimuli at brain stem and cortical levels, but little research has focused on possible functional coupling between these diverse brain areas. The present study recorded the cortical C-process [5] evoked by a pitch change between two successive tones, as well as the brain stem frequency-following response (FFR) evoked by each tone. The results replicated expected C-process component waveforms, including a late, negative (N2) component. FFR spectral intensity differences between the two tones were significantly correlated with N2 amplitude. These results suggest that signal processing reflected in long-latency auditory evoked response components is not exclusively a cortical phenomenon, but also depends upon patterns of neural processing occurring in brain stem pathways.

Acoustic Stimulation↗

PubMed2004

Brain stem evoked response to forward and reversed speech in humans.

Speech stimuli played in reverse are perceived as unfamiliar and alien-sounding, even though phoneme duration and fundamental voicing frequency are preserved. Although language perception ultimately resides in the neocortex, the brain stem plays a vital role in processing auditory information, including speech. The present study measured brain stem frequency-following responses (FFR) evoked by forward and reverse speech stimuli recorded from electrodes oriented horizontally and vertically to measure signals with putative origins in auditory nerve and rostral brain stem, respectively. The vertical FFR showed increased amplitude due to forward speech. It is concluded that familiar phonological and prosodic properties of forward speech selectively activate central brain stem neurons.

Acoustic Stimulation↗

PubMed2003

Selective attention affects human brain stem frequency-following response.

Selective attention modifies long-latency cortical event-related potentials. Amplitudes are typically enhanced and/or latencies reduced when evoking stimuli are attended. However, there is controversy concerning the effects of selective attention on short-latency brain stem evoked potentials. The objective of the present study was to assess possible attention effects on the brain stem auditory frequency-following response (FFR) elicited by a periodic tone. Young adult subjects heard a repetitive auditory stimulus while detecting infrequent target stimuli in either an auditory or visual detection task. Five channels of high frequency electroencephalographic (EEG) activity were recorded along the scalp midline with the center electrode positioned at the vertex. The FFR was elicited by the repetitive tone during both tasks. There were significant individual differences in the electrode sites yielding maximum response amplitudes, but overall FFR amplitudes were significantly larger during the auditory attention task. These results suggest that selective attention in humans can modify signal processing in sensory (afferent) pathways at the level of the brain stem. This may reflect top-down perceptual preprocessing mediated by extensive descending (efferent) pathways that originate in the cortex. Overall, the FFR appears to be a robust indicator of early auditory neural processing and shows effects not seen in brain stem auditory evoked response studies employing transient (click) acoustic stimuli.

Acoustic Stimulation↗