Biology subjects

Bartlett, E. L.

Publications and source records attributed to Bartlett, E. L..

4 recordsLinked to original sources

bioRxiv2018

Persistent activity in primate auditory cortex evoked by sensory stimulation

Persistent activity, the elevated firing of a neuron after the termination of a stimulus, is hypothesized to play a critical role in working memory. This form of activity is therefore typically studied within the context of a behavioural task that includes a working memory component. Here we investigated whether persistent activity is observed in sensory cortex and thalamus in the absence of any explicit behavioural task. We recorded spiking activity from single units in the auditory cortex (fields A1, R and RT) and thalamus of awake, passively-listening marmosets. We observed persistent activity that lasted for hundreds of milliseconds following the termination of the acoustic stimulus, in the absence of a task. Persistent activity was observed following both adapting and sustained responses during the stimulus and showed similar stimulus tuning to these evoked responses. Persistent activity was also observed following suppression in firing during the stimulus. These response types were observed across all cortical fields tested, but were largely absent from thalamus. As well as being of shorter duration, thalamic persistent activity emerged following a longer latency than in cortex, indicating that persistent activity may be generated within auditory cortex during passive listening. Given that these responses were observed in the absence of a explicit behavioural task, persistent activity in sensory cortex may have functional importance beyond storing task-relevant information in working memory.

neuroscience↗

bioRxiv2018

Aging alters envelope representations of speech-like sounds in the inferior colliculus

Hearing impairment in aging is thought to arise from impaired temporal processing in auditory circuits. We used a systems-level (scalp recordings) and a microcircuit-level (extracellular recordings) approach to investigate how aging affects the sensitivity to temporal envelopes of speech-like sounds in rats. Scalp-recorded potentials suggest an age-related increase in sensitivity to temporal regularity along the ascending auditory pathway. The underlying cellular changes in the midbrain were examined using extracellular recordings from inferior colliculus neurons. We observed an age-related increase in sensitivity to the sounds onset and temporal regularity (i.e., periodicity envelope) in the spiking output of inferior colliculus neurons, relative to their synaptic inputs (local field potentials). This relative enhancement for aged animals was most prominent for multi-unit (relative to single-unit) spiking activity. Spontaneous multi-unit, but not single-unit, activity was also enhanced in aged compared to young animals. Our results suggest that aging is associated with altered sensitivity to a sounds temporal regularities, and that these effects may be due to increased gain of neural network activity in the midbrain.

neuroscience↗

bioRxiv2017

Global State Changes Induce Non-reciprocal Reduction of Mutual Information in the Thalamocortical Network

Understanding the neural mechanisms of loss and recovery of consciousness remains an active area of scientific and clinical interest. Recent models and theories of consciousness implicate thalamus or neocortex as the dominant regions that control global state change, but experimentally testing these theories requires parsing the response properties of the complex thalamocortical network. In this work, we explore information processing using chronic recordings of multiunit activity between thalamus and cortex by targeting either the corticothalamic or thalamocortical pathway with direct electrical stimulation under subhypnotic and just-hypnotic states of isoflurane or dexmedetomidine induced unconsciousness. We found that mutual information between the stimulus and response in the corticothalamic circuit decreases with loss of consciousness, and that the change is not reciprocated in the thalamocortical direction. These changes in mutual information were moderately correlated with changes in evoked rate, and a strong effect of isoflurane on spontaneous and evoked rate accounts for a large portion of the change in mutual information. Further, we found cortical synchrony to increase under sub-and just-hypnotic doses of dexmedetomidine and isoflurane, suggesting cortical responses become more causally dependent on thalamocortical input at reduced levels of consciousness, or unconsciousness. We believe these changes suggest loss of consciousness is associated with a decrease in the number of available cortical network states, and may suggest cognitive unbinding from ascending sensory input.

neuroscience↗

bioRxiv2017

Age-related decline in behavioral discrimination of amplitude modulation frequencies compared to envelope-following responses

The ability to discriminate modulation frequencies is important for speech intelligibility because speech has amplitude and frequency modulations. Neurophysiological responses assessed by envelope following responses (EFRs) significantly decline at faster amplitude modulation frequencies (AMF) in older subjects. A typical assumption is that a decline in EFRs will necessarily result in corresponding perceptual deficits. To test this assumption, we investigated young and aged Fischer-344 rats behavioral AMF discrimination abilities and compared to their EFRs. A modified version of prepulse inhibition (PPI) of acoustic startle reflex (ASR) was used to obtain behavioral performance. A PPI trial contains pulses of sinusoidal AM (SAM) at 128 Hz presented sequentially, a SAM prepulse with different AMF and a startle-eliciting-stimulus. To account for hearing threshold shift or age-related synaptopathy, stimulus levels were presented at 10-dB lower or match to the aged peripheral neural activation (using auditory brainstem response wave I amplitude). When AMF differences and modulation depths were large, young and aged animals behavioral performances were comparable. Aged animals AMF discrimination abilities declined as the AMF difference or the modulation depth reduced, even compared to the young with peripheral matching. Young animals showed smaller relative decreases in EFRs with reduced modulation depths. The correlation of EFRs and AM perception was identified to be more consistent in young animals. The overall results revealed larger age-related deficits in behavioral perception compared to EFRs, suggesting additional factors that affect perception despite smaller degradation in neural responses. Hence, behavioral and physiological measurements are critical in unveiling a more complete picture on the auditory function.

neuroscience↗