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Biomedical subjects

T H Harding

Publications and source records attributed to T H Harding.

6 recordsLinked to original sources
PubMed1987

Recovery of the visual evoked response in the cat following administration of diisopropylfluorophosphate, an irreversible cholinesterase inhibitor.

Visual evoked responses (VER) to counterphased gratings were recorded from area 17 of cat visual cortex prior to and following administration of diisopropylfluorophosphate (DFP). The VER and acetylcholinesterase (AChE) activity of blood, retina, and visual cortex were reduced significantly following DFP administration. Approximately two hours after exposure to 4 mg/kg DFP, the VER began to recover and in some cats returned to base line levels. In contrast, blood, retina, and cortex AChE activity showed little, if any, tendency for recovery throughout the experiment. Since atropine sulfate provided at least partial recovery of the VER following DFP without affecting AChE inhibition, an accumulation of acetylcholine (ACh) probably is involved in the initial visual loss. However, recovery of the VER over time while AChE remained severely inhibited implicates mechanisms other than, or in addition to, accumulation of ACh at receptor sites.

Acetylcholinesterase↗
PubMed1985

The effects of diisopropylfluorophosphate on spatial frequency responsivity in the cat visual system.

Visual-evoked responses to counterphased gratings were recorded from area 17 of cat visual cortex before and after diisopropylfluorophosphate (DFP) administration. DFP produced effects similar to those obtained following physostigmine sulfate administration, in that responses to low spatial frequencies were preferentially reduced. The time course of the effects was quite different for the two types of drugs, and for high doses of DFP responses to all spatial frequencies were approximately uniformly depressed or abolished.

Animals↗
PubMed1979

Visual resolution and receptive field size: examination of two kinds of cat retinal ganglion cell.

Intraocular recordings from brisk-sustained and brisk-transient ganglion cells in the cat's retina revealed a systematic increase in center size and decrease in spatial cut-off frequency with increasing distance from the area centralis. At any one eccentricity sizes of the centers of sustained and transient cells did not overlap, and the variation in cut-off frequency for each class was constrained to about one-half octave.

Animals↗
PubMed1976

Monkey contrast threshold for aperiodic patterns.

A monkey's and a human subject's threshold responses were measured for single- and double-bar patterns of high spatial frequency. The observed values were compared to predicted values which were derived from each subject's contrast sensitivity function. A theoretical peak-to-trough threshold mechanism was assumed in the calculations. The threshold predictions, which are couched in the assumption that the spatial visual system is linear near its threshold, were found to be close to observed values. The results are interpreted to suggest that the monkey visual system analyzes spatial information in qualitatively and quantitatively similar ways to human, and that a linear theory may be used for analyses of primate vision.

Animals↗