Biomedical subjects

Steven J Eliades

Publications and source records attributed to Steven J Eliades.

3 recordsLinked to original sources

PubMed2005

Dynamics of auditory-vocal interaction in monkey auditory cortex.

Single neurons in the primate auditory cortex exhibit vocalization-related modulations (excitatory or inhibitory) during self-initiated vocal production. Previous studies have shown that these modulations of cortical activity are variable in individual neurons' responses to multiple instances of vocalization and diverse between different cortical neurons. The present study investigated dynamic patterns of vocalization-related modulations and demonstrated that much of the variability in cortical modulations was related to the acoustic structures of self-produced vocalization. We found that suppression of single unit activity during multi-phrased vocalizations was temporally specific in that it was maintained during each phrase, but was released between phrases. Furthermore, the degree of suppression or excitation was correlated to the mean energy and frequency of the produced vocalizations, accounting for much of the response variability between multiple instances of vocalization. Simultaneous recordings of pairs of neurons from a single electrode revealed that the modulations by self-produced vocalizations in nearby neurons were largely uncorrelated. Additionally, vocalization-induced suppression was found to be preferentially distributed to upper cortical layers. Finally, we showed that the summation of all auditory cortical activity during vocalization, including both single and multi-unit responses, was weakly excitatory, consistent with observations from studies of the human brain during speech.

Acoustic Stimulation↗

PubMed2005

Wireless multichannel biopotential recording using an integrated FM telemetry circuit.

This paper presents a four-channel telemetric microsystem featuring on-chip alternating current amplification, direct current baseline stabilization, clock generation, time-division multiplexing, and wireless frequency-modulation transmission of microvolt- and millivolt-range input biopotentials in the very high frequency band of 94-98 MHz over a distance of approximately 0.5 m. It consists of a 4.84-mm2 integrated circuit, fabricated using a 1.5-microm double-poly double-metal n-well standard complementary metal-oxide semiconductor process, interfaced with only three off-chip components on a custom-designed printed-circuit board that measures 1.7 x 1.2 x 0.16 cm3, and weighs 1.1 g including two miniature 1.5-V batteries. We characterize the microsystem performance, operating in a truly wireless fashion in single-channel and multichannel operation modes, via extensive benchtop and in vitro tests in saline utilizing two different micromachined neural recording microelectrodes, while dissipating approximately 2.2 mW from a 3-V power supply. Moreover, we demonstrate successful wireless in vivo recording of spontaneous neural activity at 96.2 MHz from the auditory cortex of an awake marmoset monkey at several transmission distances ranging from 10 to 50 cm with signal-to-noise ratios in the range of 8.4-9.5 dB.

Action Potentials↗

PubMed2002

Sensory-motor interaction in the primate auditory cortex during self-initiated vocalizations.

Little is known about sensory-motor interaction in the auditory cortex of primates at the level of single neurons and its role in supporting vocal communication. The present study investigated single-unit activities in the auditory cortex of a vocal primate, the common marmoset (Callithrix jacchus), during self-initiated vocalizations. We found that 1) self-initiated vocalizations resulted in suppression of neural discharges in a majority of auditory cortical neurons. The vocalization-induced inhibition suppressed both spontaneous and stimulus-driven discharges. Suppressed units responded poorly to external acoustic stimuli during vocalization. 2) Vocalization-induced suppression began several hundred milliseconds prior to the onset of vocalization. 3) The suppression of cortical discharges reduced neural firings to below the rates expected from a unit's rate-level function, adjusted for known subcortical attenuation, and therefore was likely not entirely caused by subcortical attenuation mechanisms. 4) A smaller population of auditory cortical neurons showed increased discharges during self-initiated vocalizations. This vocalization-related excitation began after the onset of vocalization and is likely the result of acoustic feedback. Units showing this excitation responded nearly normally to external stimuli during vocalization. Based on these findings, we propose that the suppression of auditory cortical neurons, possibly originating from cortical vocal production centers, acts to increase the dynamic range of cortical responses to vocalization feedback for self monitoring. The excitatory responses, on the other hand, likely play a role in maintaining hearing sensitivity to the external acoustic environment during vocalization.

Acoustic Stimulation↗