Biomedical subjects

Kathleen M Carter

Publications and source records attributed to Kathleen M Carter.

3 recordsLinked to original sources

PubMed2005

Local functional state differences between rat cortical columns.

Surface evoked potentials (SEPs) during auditory clicks and whisker twitches are usually larger during quiet sleep (QS) over waking and REM sleep. However, SEP amplitudes from single trials fluctuate periodically between high and low values regardless of sleep-wake cycle. To test the hypothesis that state-independent fluctuations represent local functional sleep-like states of individual cortical columns, we examined single trial SEP amplitudes from multiple cortical locations across sleep-wake cycles. Bilateral stimuli produced SEP amplitude fluctuations in each hemisphere that usually covaried (r = 0.4), but with frequent hemispheric differences. Two neighboring whiskers, twitched simultaneously on the same side, produced highly correlated SEPs in neighboring cortical columns (r = 0.9) with frequent divergences. We found 50% more disparity during QS over waking, indicating that the differences did not result from recording noise or stimulus inconsistency. Local SEP fluctuations also followed local differences in the delta wave signal during QS (r = 0.4), suggesting that similar mechanisms may modulate the SEP. The duration of the localized sleep-like (high SEP amplitude) state was dependent on the duration of prior wake-like (low SEP amplitude) state (r = 0.5), suggesting a use dependence of prior functional state period. Since SEP indicators fluctuated independently from whole animal sleep state, and were frequently different between hemispheres and nearby cortical columns, these data support the theory that sleep-like functional states may be localized to brain regions at least as small as cortical columns.

Acoustic Stimulation↗

PubMed2005

Spatio-temporal mapping of rat whisker barrels with fast scattered light signals.

Optical techniques offer a number of potential advantages for imaging dynamic spatio-temporal patterns of activity in neural tissue. The methods provide the wide field of view required to image population activation across networks, while allowing resolution of the detailed structure of individual cells. Optical probes can provide high temporal resolution without penetrating the tissue surface. However, functional optical imaging has been constrained by the small size of the signals and the sluggish nature of the metabolic and hemodynamic responses that are the basis of most existing methods. Here, we employ both high-speed CCD cameras and high-sensitivity photodiodes to optimize resolution in both space and time, together with dark-field illumination in the near-infrared, to record fast intrinsic scattering signals from rat somatosensory cortex in vivo. Optical responses tracked the physiological activation of cortical columns elicited by single whisker twitches. High-speed imaging produced maps that were initially restricted in space to individual barrels, and then spread over time. Photodiode recordings disclosed 400-600 Hz oscillatory responses, tightly correlated in frequency and phase to those seen in simultaneous electrical recordings. Imaging based on fast intrinsic light scattering signals eventually could provide high resolution dynamic movies of neural networks in action.

Animals↗

PubMed2004

Simultaneous birefringence and scattered light measurements reveal anatomical features in isolated crustacean nerve.

Simultaneous fast birefringence and scattered light changes associated with crustacean nerve activation have different time courses and are produced by separate biophysical mechanisms. Technological advances in illumination, photodiodes and amplification circuitry achieved better signal-to-noise than earlier studies revealing optical signals in axonal nerve bundles as small as crayfish ventral cord and claw. The birefringence measurements yielded signals that could be observed in single trials, with temporally separated peaks associated with axonal populations of different diameters. A slit aperture placed perpendicular to the nerve reduced the spatial-temporal integration and enhanced the temporal structure of the separate peaks in the birefringence signal. Moving the slit aperture farther from the stimulation point delayed the signal in time, and also enhanced the separation between peaks. Different propagation velocities of the separate peaks provided evidence for at least three neuronal populations in the bundle. These studies underscore the advantages of birefringence over scattering measurements. Application of birefringence methods can optimize non-invasive imaging techniques being developed to detect fast optical responses associated with electrical neural activity in humans.

Animals↗