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R T Marrocco

Publications and source records attributed to R T Marrocco.

At least 37 records · Page 2Linked to original sources
PubMed1982

Is there a high concentration of color-selective cells in area V4 of monkey visual cortex?

1. Recordings were made from neurons located within the central-field representation of the V4 area of extrastriate visual cortex using a semichronic, nitrous-oxide preparation; the properties of 174 cells were examined in sufficient detail to permit their classification. Cyto- and myeloarchitectural studies confirmed the identification of the area. 2. Color-selective cells with either color-biased or color-opponent properties represented about 20% of the examined population. Their incidence was not significantly different from that of similar cells encountered in penetrations into the central-field representation of area V2. 3. Most color-selective cells had color-biased properties, responding best to wave-lengths shorter than 460 nm, or longer than 580 n, or both. No examples of "green-biased" cells were found. Some color-biased cells responded to photopically matched white light, while others did not. Very few cells showed overt color-opponent responses. The spectral sensitivity of color-selective cells was not unusually narrow. 4. Cells lacking color selectivity and responding equally well to chromatic and achromatic lights of equal photopic luminosity, were the most commonly encountered cell type in penetrations of different parts of the V4 area (56%). Other than color, these cells showed stimulus preferences like those of color-selective cells. 5. One-fourth of V4 cells could not be systematically driven with the various stimuli used. This finding is consistent with recent results of recordings from the prelunate gyrus of the behaving monkey suggesting that some V4 cells receive extraretinal signals. 6. Our results do not support recent claims that V4 is specialized in the detailed analysis of color information.

Animals↗
PubMed1982

Modulation of lateral geniculate nucleus cell responsiveness by visual activation of the corticogeniculate pathway.

A radial grating stimulus was used to assess the effect of stimulation of the region beyond the classical surround of monkey lateral geniculate nucleus (LGN) receptive fields. The effect was measured by the differences in the responsiveness of the LGN cell center to small flashing spots between two conditions: (1) grating stationary or (2) grating rotating. The grating was present only in regions beyond the classical center and surround. The rotating grating produced changes in the flash-evoked spike response but not in the spontaneous activity in about half of the X cells and all of the Y cells. The direction of the effect was independent of the sign of the receptive field center. In a control experiment, cryogenic blockade of striate cortex reversed the effect in all cells tested. The grating effect was still present for cells having fields in that part of visual space beyond the region represented by the cooled cortical area. The effect was not a result of activation of classical extra-receptive field influences, since cells showing the effect did not exhibit shift or periphery effects or outer disinhibitory surrounds. The effect was not seen in recordings from intrageniculate retinal axons. We conclude that the radial grating effects LGN cell responsivity by activation of the corticogeniculate pathway.

Animals↗
PubMed1982

Spatial summation and conduction latency classification of cells of the lateral geniculate nucleus of macaques.

Cells in the lateral geniculate nucleus (LGN) of the macaque monkey were investigated with microelectrodes in an attempt to develop an overall classification scheme. We classified cells in the parvocellular (P) and magnocellular (M) layers according to (non)linearity of spatial summation, shock latency, and chromatic organization of center and surround. We also measured the spatial and temporal tuning to counterphasing and drifting sine wave gratings and tested for periphery effects. Our results showed that no strict laminar segregation existed for any cell property studied. Our results can be summarized as follows: 1. Most P layer cells showed a linear summation (98%) and color-opponent responses (80%), while other cells showed a nonlinear summation (Y-cells, 2%) and broad band responses (28%). In contrast, 37% of the M layer cells were linear summators and the remainder were nonlinear. Therefore, there are overlapping distributions of X- and Y-cells in P and M layers but not a strict segregation. 2. P layer cells had longer shock latencies than M layer cells. X-cells conducted more slowly (2.4 +/- 0.7 msec) than Y-cells (1.6 +/- 0.8 msec), but there were overlapping distributions. Latency shortened gradually, rather than abruptly, with increasing depth. 3. The first harmonic of X- and Y-cell responses was maximally sensitive to spatial frequencies of about 2 cycles/deg. Each type of cell modulated about a mean rate to a drifting grating, although Y-cells had higher distortion than X-cells. Response amplitudes to drifting gratings were higher for MX- and MY- than for PX-cells. No DC elevation to high spatial frequencies was seen. Spatial bandwidths averaged 2 to 5 octaves. X-cells were maximally tuned to temporal frequencies around 11 Hz, and Y-cells were tuned to about 19 Hz;. temporal bandwidths for both averaged 2.8 octaves. 4. Periphery effects were detected in 4% of the X-cells and 25% of the Y-cells. 5. These data indicate that gradual changes occur between dorsal and ventral layers: summation changes from linear to nonlinear; conduction latencies shorten; peak temporal tuning increases; response amplitudes increase; the periphery effect becomes more prevalent. Spatial tuning does not change. No strict laminar segregation or specificity exists for any of the properties that we studied.

Animals↗
PubMed1978

Saccades induced by stimulation of the frontal eye fields: interaction with voluntary and reflexive eye movements.

Saccadic eye movements were evoked in alert monkeys by electrical stimulation of the frontal eye fields (FEF). The interaction of FEF movements with voluntary saccades, pursuit, and vestibular nystagmus (VN) was examined. An FEF saccade in one direction could be evoked as little as 10 msec after the onset of a natural rapid movement (saccade, fast phase of VN) in the opposite direction. Thus, refractory periods between similar eye movements are directionally specific. The frequency of evoked FEF saccades following natural slow movements (pursuit, slow phase of VN) in either direction was reduced as though saccade thresholds were elevated. The FEF appears capable of modulating any ongoing eye movement.

Animals↗
PubMed1977

Monkey superior colliculus: properties of single cells and their afferent inputs.

1. Receptive-field (RF) properties of 212 single cells in the superior colliculus of paralyzed macaque monkeys were studied with microelectrodes. Units were divided into superficial (0-1 mm) and deep (1-2.5 mm) layers. Orthodromic action potentials were evoked in these cells by shocking optic chiasm. 2. The vast majority of superficial cells responded to stationary or moving stimuli with transient bursts of activity and were nondirectionally selective. Moving stimuli were most effective and three main cell groups, based on response patterns to leading and trailing stimulus edges, were identified. 3. All cells had chromatically nomopponent RFs, as judged by their spectral response functions in the presence of neutral and chromatic backgrounds and on their lack of response to moving, equal-luminance chromatic borders. 4. With the exception of some very short and very long values, orthodromic latencies were unimodally distributed with a mean of 7.8 ms. The prime determinant of a cell's latency was its depth below the collicular surface rather than a specific RF feature. 5. Cells with shorter latencies (located in superficial layers) were able to reliably signal high-velocity stimulus movement; those with longer latencies (located in deeper layers) reliably signaled low-velocity motion only. 6. Results support the hypothesis that response latency is related to differences in RF organization between layers.

Afferent Pathways↗
PubMed1976

Sustained and transient cells in monkey lateral geniculate nucleus: conduction velocites and response properties.

The receptive-field properties of units in the macaque LGN were studied with extracellular microelectrodes. Analysis of responses of opponent and nonopponent cells to stationary spots, moving spots, and grating revealed transient and sustained varieties of both spectral groups as well as cells with mixed properties. The cell's temporal discharge pattern was not correlated with its color sensitivity. Cells that ere classified as sustained responders did so under all stimulus conditions tested. Most transient cells responded in a transient fashion to each stimulus tested. In a few cells, a sustained response could be shortened into a transient response by activating the cell's surroun mechanism. The conduction velocities of sustained and transient cells were determined by shocking optic chiasm and striate cortex. Among nonopponent cells, transient types conducted significantly faster than the sustained type. No such difference was found among opponent cells. Among all cells, the fastest conducting were transient nonopponent (14 m/s), while the slowest were +B-Y opponent cells (4 m/s). Intermediate were sustained nonopponent (11 m/s) and the remainder of opponent cells types (about 7 m/s). There was a significant positive correlation between a cell's shock-evoked spike latency and its visually evoked latency. These results suggest that there are at least three independent information channels in monkey geniculostriate pathway. Further characterization of these channels is in progress.

Animals↗
PubMedDate not supplied

Attention as a target of intoxication: insights and methods from studies of drug abuse.

A symposium was convened to discuss recent developments in the assessment of attention and the effects of drugs and toxic chemicals on attention at the 17th annual meeting of the Behavioral Toxicology Society on May 1, 1999, in Research Triangle Park, NC. Speakers addressed issues including the methodology of assessing cognitive function, the neurobiology of specific aspects of attention, the dual roles of attention as a target of intoxication and as a mediating variable in the development of addiction to psychoactive drugs, the changes in attention that accompany neuropsychological disorders of schizophrenia, senile dementia of the Alzheimer type and attention deficit hyperactivity disorder, and potential therapies for these disorders. This article provides an overview of the objectives of the symposium, followed by summaries of each of the talks given.

Animals↗