John K. Stevens

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Serial electron microscopy and 3-D reconstructions of dendritic spines from hippocampal area CA 1 dendrites were obtained to evaluate 2 questions about relationships between spine geometry and synaptic efficacy. First, under what biophysical conditions are the spine necks likely to reduce the magnitude of charge transferred from the synapses on the spine(More)
We have used serial electron microscopy and 3-dimensional reconstructions of dendritic spines from Purkinje spiny branchlets of normal adult rats to evaluate 2 questions about the relationship of spine geometry to synaptic efficacy. First, do relationships between spine geometry and other anatomical indicators of synaptic activity suggest that spine size(More)
We have studied 15 bipolar neurons from a small patch (14 X 120 micron) of adult cat retina located within the area centralis. From electron micrographs of 189 serial ultrathin sections, the axon of each bipolar cell was substantially reconstructed with its synaptic inputs and outputs by means of a computer-controlled reconstruction system. Based on(More)
In darkness, observers partially paralyzed with curare make large (greater thn 20 degrees) gaze- and dosage-dependent errors in visually localizing eye-level-horizontal and median planes, in matching the location of a sound to a light, and in pointing at a light. In illuminated, structured visual localization and pointing are accurate but errors in(More)
We reconstructed from electron micrographs of 189 serial ultrathin sections a major portion of the dendritic tree of an on-beta ganglion cell through its sixth order of branching. One hundred three contacts from three cone bipolar cells were identified. Forty-seven contacts were from a single CBb1 cone bipolar. These were distributed widely over the(More)
Spatial and temporal properties of LGN receptive fields were studied by flashing a small bar of light across the field in 28 discrete steps. The flashes at each of the spatial positions were used to produce 28 PST histograms. These histograms were in turn displayed as a plane, with space on the chi axis, time on the psi axis, and probability of firing on(More)
Serial sections were made of several excitatory nerve terminals in the stretcher muscle of the spider crab, Hyas areneus , to document locations of inhibitory axoaxonal synapses responsible for physiologically powerful presynaptic inhibition. The excitatory terminals are varicose, often with small side branches joined to the main terminal by thin(More)
AI and AII cat retinal amacrine cells have highly varicose non-uniform, neuritic processes. Processes of both types were reconstructed via a computer system using serial electron micrographs. These reconstructions were analyzed for (a) varicosity volume, surface area, and length, (b) "neck" volume, surface area, and length, (c) number of microtubules within(More)
Subparalytic doses of s were given to three observers. Four major perceptions were reported: (1) displacement or repostttonmg,of the perceived visual world in the direction of a successfully executed eve movement: (2) jumping durmg a saccade; (3) mocmrent associated with drift of the eye; (4) increased effort associated with each eye movement. Paralytic(More)
Amacrine dendritic varicosities from cat retina were reconstructed using serial electron micrographs. Each varicosity contained a synaptic input and a synaptic output, suggesting that they may function as isolated local circuits. A passive steady state electrical model demonstrated that for a given conductance change the varicose dendrite maximizes the(More)