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R C deCharms

Publications and source records attributed to R C deCharms.

5 recordsLinked to original sources
PubMed2000

Neural representation and the cortical code.

The principle function of the central nervous system is to represent and transform information and thereby mediate appropriate decisions and behaviors. The cerebral cortex is one of the primary seats of the internal representations maintained and used in perception, memory, decision making, motor control, and subjective experience, but the basic coding scheme by which this information is carried and transformed by neurons is not yet fully understood. This article defines and reviews how information is represented in the firing rates and temporal patterns of populations of cortical neurons, with a particular emphasis on how this information mediates behavior and experience.

Animals↗
PubMed1999

A multielectrode implant device for the cerebral cortex.

A new class of brain implant technology was developed that allows the simultaneous recording of voltage signals from many individual neurons in the cerebral cortex during cognitive tasks. The device allows recording from 49 independent positions spanning a 2 x 2-mm region of neural tissue. The recording electrodes are positioned in a square grid with 350 microm spacing, and each microelectrode can be precisely independently vertically positioned using a hydraulic microdrive. The device utilizes ultrafine, sharp iridium microelectrodes that minimize mechanical disturbance of the region near the electrode tip and produce low noise neuronal recordings. The total weight of this device is less than 20 g, and the device is reusable. The implant device has been used for transdural recordings in primary somatosensory and auditory cortices of marmosets, owl monkeys, and rats. On a typical day, one-third of the microelectrodes yield well-discriminated single neuron action potential waveforms. Additional array electrodes yield lower amplitude driven multiunit activity. The average signal-to-noise ratio of discriminated action potential waveforms 6 months after implantation was greater than 9. Simple design alternatives are discussed that can increase the number of electrodes in the array and the depths at which dense array recordings can be achieved.

Animals↗
PubMed1998

Optimizing sound features for cortical neurons.

The brain's cerebral cortex decomposes visual images into information about oriented edges, direction and velocity information, and color. How does the cortex decompose perceived sounds? A reverse correlation technique demonstrates that neurons in the primary auditory cortex of the awake primate have complex patterns of sound-feature selectivity that indicate sensitivity to stimulus edges in frequency or in time, stimulus transitions in frequency or intensity, and feature conjunctions. This allows the creation of classes of stimuli matched to the processing characteristics of auditory cortical neurons. Stimuli designed for a particular neuron's preferred feature pattern can drive that neuron with higher sustained firing rates than have typically been recorded with simple stimuli. These data suggest that the cortex decomposes an auditory scene into component parts using a feature-processing system reminiscent of that used for the cortical decomposition of visual images.

Acoustic Stimulation↗
PubMed1996

Primary cortical representation of sounds by the coordination of action-potential timing.

Cortical population coding could in principle rely on either the mean rate of neuronal action potentials, or the relative timing of action potentials, or both. When a single sensory stimulus drives many neurons to fire at elevated rates, the spikes of these neurons become tightly synchronized, which could be involved in 'binding' together individual firing-rate feature representations into a unified object percept. Here we demonstrate that the relative timing of cortical action potentials can signal stimulus features themselves, a function even more basic than feature grouping. Populations of neurons in the primary auditory cortex can coordinate the relative timing of their action potentials such that spikes occur closer together in time during continuous stimuli. In this way cortical neurons can signal stimuli even when their firing rates do not change. Population coding based on relative spike timing can systemically signal stimulus features, it is topographically mapped, and it follows the stimulus time course even where mean firing rate does not.

Action Potentials↗