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D A Pollen

Publications and source records attributed to D A Pollen.

At least 37 records · Page 2Linked to original sources
PubMed1981

Intracortical microstimulation of neurons in the visual cortex of the cat.

The response of visual cortex neurons to local intracortical microstimulation was measured in the anesthetized cat. When the recording microelectrode was very close (about 20 micrometers) to the tip of the stimulating electrode, threshold currents as low as 10 micro A were capable of firing neurons. Over a 20-fold range in distance from the site of stimulation, an 80-fold increase in threshold current was observed. The mean latency of activation for 30 neurons tested with intracortical stimulation was 2.88 +/- 0.45 msec. The majority of these cells were probably synaptically activated. The mean threshold current for these neurons was 0.55 +/- 0.12 mA (N = 30). These values were significantly smaller than the thresholds found previously when stimulating electrodes were located on the pia-arachnoid surface of the visual cortex.

Animals↗
PubMed1979

Relationship between spatial frequency selectivity and receptive field profile of simple cells.

1. Receptive fields of simple cells in area 17 of the cat were mapped with stationary stimuli. Spatial frequency selectivities of the same cells were measured with drifting sinusoidal gratings. 2. The reconstructed field profile (inverse Fourier transform of selectivity curve) shows qualitative agreement with the mapped profile, and suggests the existence of additional side-lobes in the field. The side-lobes may correspond to the 'unresponsive regions' investigated by Maffei & Fiorentini (1976). 3. Our data suggest that the simple cell may perform approximately linear spatial summation of inputs to the visual system. However, the output of the simple cell is generally non-linear as reflected in its truncated responses to gratings.

Animals↗
PubMed1979

Spatial periodicities of periodic complex cells in the visual cortex cluster at one-half octave intervals.

Within individual penetrations in the visual cortex, spatial periodicities of periodic complex cells differ by either one-half or one octave. When data are pooled from neurons subserving the central visual area in many cats, the results indicate that spatial periodicities cluster at one-half octave intervals over a 2 1/2-octave range (0.95 to 5.4 cyc/deg). Thus a relatively small number of such channels spaced at regular intervals along a logarithmic scale within each orientation column may suffice for this stage of spatial processing.

Animals↗
PubMed1977

Responses of single neurons to electrical stimulation of the surface of the visual cortex.

We have recorded from single neurons in the visual cortex of the cat while stimulating the cortical surface with the same type of electrodes and the same parameters of stimulation which have produced phosphenes in conscious man. Parameters of stimulation which will permit excitation of single cortical neurons with little risk of producing afterdischarges are described. The patterns of excitation of single neurons during surface stimulation and the effects of stimulation on neuroglial cells have also been studied. Surface stimulation also produced marked alterations in cortical excitability as tested with visually presented stimuli. Mechanisms by which single neurons are excited by surface stimulation are also considered.

Action Potentials↗
PubMed1976

Responses of complex cells in the visual cortex of the cat as a function of the length of moving slits.

(1) As a step towards specifying the spatial selectivity characteristics of complex cells with spatially periodic substructures, we have studied single cell responses to narrow slits of variable length moved across the receptive field in the preferred direction. In general, the length-response curves were linear over a considerable and sometimes full range until an optimal slit length was reached. (2) In those cells in which the rate of rise of the slit length-response functions decreased before the optimal length was reached, at least 3 factors contribute to the shape of the curve. First, the receptive field shapes of some complex cells are more ovoid or rounded than rectangular, and the summation of responses from excitatory zones of varying optimal lengths itself results in a nonlinear slit length-response function at long slit lengths. Second, central regions may contribute more to cell response than do more lateral regions along the length dimension. Third, a nonlinearity in the slit length-response curve may occur in the upper range of slit lengths as a saturation effect because discharge rates may reach 600/sec, which appears to be close to a limiting firing rate. (3) Some cells believed to be complex during preliminary receptive field testing showed weak inhibitory regions beyond the region of the optimal slit length. Many of these cells also displayed periodic average response histograms to moving slits. The extent and magnitude of the inhibition were variable from cell to cell. In terms of receptive field properties, these cells and 'regular' complex cells seem part of a continuum.

Animals↗
PubMed1975

Periodic excitability changes across the receptive fields of complex cells in the striate and parastriate cortex of the cat.

1. Complex cells in cortical areas 17 and 18 of the cat have been studied in response to narrow slits and edges moving across the receptive field in the preferred direction and also to stationary slits of different widths. 2. Average response histograms, recorded as a narrow slit was moved across the receptive field, displayed a periodic series of peaks above a base line level. The response histogram for most area 17 and 18 cells contained five principal peaks; sometimes one or two weaker peaks were present at receptive field borders. The histogram for one cell located at the area 17-18 border showed thirteen distinct peaks. Periodic response patterns were also generated as an extended edge was moved across the receptive field. Plots of cell responses versus slit width for stationary slits of different widths also indicated periodic response pattern. 3. The accuracy of determining the preferred slit orientation was the single most important requirement for demonstrating the periodic response pattern. Significant changes in the appearance of the periodic pattern occurred even upon 5 degrees rotations away from the preferred orientation. 4. Average response histograms were also studied over a wide range of moving slit velocities. The number of peaks across corresponding spacings within the recewptive field remained constant over a range of velocities. Response amplitudes, however, were velocity dependent. Thus the response peaks remain associated with fixed positions within visual space independent of stimulus velocity, even though temporal as well as spatial factors may be involved in response selectivity and the periodic modulation. The most striking periodic response histograms were generated at the velocities which produced the greatest cell firing rates. Area 17 complex cells responded well to velocities of less than 0-5 degrees to 6-0 degrees/sec, but cells in area 18 generally required higher velocities, sometimes as high as 20 degrees--30 degrees/sec, for a good response. 5. Spatial frequencies for the periodic component of the receptive field for area 17 cells in the central visual area covered a range of three octaves up to 5 cycles/degree, and area 18 cells included another octave on the low frequency side. The spatial frequency of a cell was found to be roughly inversely proportional to the receptive field width. Only a small sample of area 18 cells was studied, but these cells tended to represent low spatial frequencies and to respond selectively to high velocity stimuli...

Action Potentials↗
PubMed1971

How does the striate cortex begin the reconstruction of the visual world?

The striate cortex transforms the topographic representation of visual space in the lateral geniculate body into a Fourier transform or frequency representation at the complex cell level via the intermediary simple cell stage of "strip integration." Each of these three stages contains essentially the same amount of information, which expresses a conservation of information principle; however, the form of the information is changed. In the transform domain, invariant descriptions of visual objects can be derived to serve as the basic sets required for pattern recognition and memory. We believe that our experimental and theoretical findings are fundamental for understanding the functional organization of the striate cortex.

Animals↗
PubMed1970

Neuroglia: biophysical properties and physiologic function.

The membrane time constant of neocortical glial cells is abolut 385 microseconds, less than one-twentieth the known value for the Betz cell. Glial membrane specific resistance is low (approximately 200 to 500 ohm centimeters squared. Neuroglial cells are ideally suited to buffer the immediate extraneuronal space at areas of synaptic contact against the increases in external potassium ion concentration that accompany postsynaptic and spike activity and to minimize the spread of potassium ions to other pre- and postsynaptic regions.

Animals↗
PubMed1970

Neuroglia: gliosis and focal epilepsy.

Normal neuroglial cells buffer the extracellular space around neurons and presynaptic terminals against increases in potassium ions. Epileptic foci resulting from brain injury are characterized by areas of intense fibrillary gliosis bordering neuronal tissue. The known pathological changes that occur in gliosis may impair glial control of extracellular potassium ions and lead to excessively excitable neuronal border regions.

Cicatrix↗
PubMed1968

Electrotonic spread of dendritic potentials in feline pyramidal cells.

In pyramidal cells synaptic activation of the entire apical dendritic tree distal to the branch point of the major shaft can dominate the neuronal firing pattern. Uniform synaptic activation of distant parts of the dendritic tree (~ 750 microns from the soma) would produce potential changes at the soma of 2 to 3 percent of the magnitude of the dendritic potential changes. Even these small somatic potential changes could modulate the frequency of firing of neurons depolarized close to or above firing level by more proximal synaptic inputs.

Animals↗
PubMed1967

Electrical recordings from meningioma cells during cytolytic action of antibody and complement.

Resting membrane potential and total cell resistance of human meningioma cells in tissue culture have been measured with fine microelectrodes. Addition of either antiserum inactivated with heat or control serum from normal rabbits produced small depolarizations (2 to 4 millivolts) with no discernible ( 5 percent) change in resistance. Addition of antiserums with complement, however, produced larger depolarizations and decreases in resistance before any changes in cell morphology were visible with light microscopy; as cytoplasmic swelling progressed, membrane potential dropped close to zero, and resistance decreased five- to tenfold. The electrical recording technique may be useful in the study of sublethal as well as lethal damage to immune cells and, in particular, may permit temporal resolution of damaging events and repair mechanisms in a single cell.

Antibodies↗