Biomedical subjects

Kaj Djupsund

Publications and source records attributed to Kaj Djupsund.

3 recordsLinked to original sources

PubMed2006

Flexible polyimide microelectrode array for in vivo recordings and current source density analysis.

This work presents implantable, flexible polymer-based probes with embedded microelectrodes for acute and chronic neural recordings in vivo, as tested on rodents. Acute recordings using this array were done in mice under urethane anesthesia and compared to those made using silicon-based probes manufactured at the Center for Neural Communication Technology, University of Michigan. The two electrode arrays yielded similar results. Recordings with chronically implanted polymer-based electrodes were performed for 60 days post-surgically in awake, behaving rats. The microelectrodes were used to monitor local field potentials and capture laminar differences in function of cortex and hippocampus, and produced response waveforms of undiminished amplitude and signal-to-noise ratios 8 weeks after chronic implantation. The polymer-based electrodes could also be connected to a lesion current to mark specific locations in the tissue. Current source density (CSD) analysis from the recordings depicted a source - sink-composition. Tissue response was assessed 8 weeks after insertion by immunochemical labeling with glial fibrillary acidic protein (GFAP) to identify astrocytes, and histological analysis showed minimal tissue reaction to the implanted structures.

Animals↗

PubMed2003

Asymmetric temporal properties in the receptive field of retinal transient amacrine cells.

The speed of signal conduction is a factor determining the temporal properties of individual neurons and neuronal networks. We observed very different conduction velocities within the receptive field of fast-type On-Off transient amacrine cells in carp retina cells, which are tightly coupled to each other via gap junctions. The fastest speeds were found in the dorsal area of the receptive fields, on average five times faster than those detected within the ventral area. The asymmetry was similar in the On- and Off-part of the responses, thus being independent of the pathway, pointing to the existence of a functional mechanism within the recorded cells themselves. Nonetheless, the spatial decay of the graded-voltage photoresponse within the receptive field was found to be symmetrical, with the amplitude center of the receptive field being displaced to the faster side from the minimum-latency location. A sample of the orientation of varicosity-laden polyaxons in neurobiotin-injected cells supported the model, revealing that approximately 75% of these processes were directed dorsally from the origin cells. Based on these results, we modeled the velocity asymmetry and the displacement of amplitude center by adding a contribution of an asymmetric polyaxonal inhibition to the network. Due to the asymmetry in the conduction velocity, the time delay of a light response is proposed to depend on the origin of the photostimulus movement, a potentially important mechanism underlying direction selectivity within the inner retina.

Amacrine Cells↗

PubMed2002

Temporal specificity in the cortical plasticity of visual space representation.

The circuitry and function of mammalian visual cortex are shaped by patterns of visual stimuli, a plasticity likely mediated by synaptic modifications. In the adult cat, asynchronous visual stimuli in two adjacent retinal regions controlled the relative spike timing of two groups of cortical neurons with high precision. This asynchronous pairing induced rapid modifications of intracortical connections and shifts in receptive fields. These changes depended on the temporal order and interval between visual stimuli in a manner consistent with spike timing-dependent synaptic plasticity. Parallel to the cortical modifications found in the cat, such asynchronous visual stimuli also induced shifts in human spatial perception.

Action Potentials↗