Biomedical subjects

Bogdan Dreher

Publications and source records attributed to Bogdan Dreher.

3 recordsLinked to original sources

PubMed2006

'Simplification' of responses of complex cells in cat striate cortex: suppressive surrounds and 'feedback' inactivation.

In mammalian striate cortex (V1), two distinct functional classes of neurones, the so-called simple and complex cells, are routinely distinguished. They can be quantitatively differentiated from each other on the basis of the ratio between the phase-variant (F1) component and the mean firing rate (F0) of spike responses to luminance-modulated sinusoidal gratings (simple, F1/F0 > 1; complex, F1/F0 < 1). We investigated how recurrent cortico-cortical connections affect the spatial phase-variance of responses of V1 cells in the cat. F1/F0 ratios of the responses to optimally oriented drifting sine-wave gratings covering the classical receptive field (CRF) of single V1 cells were compared to those of: (1) responses to gratings covering the CRFs combined with gratings of different orientations presented to the 'silent' surrounds; and (2) responses to CRF stimulation during reversible inactivation of postero-temporal visual (PTV) cortex. For complex cells, the relative strength of the silent surround suppression on CRF-driven responses was positively correlated with the extent of increases in F1/F0 ratios. Inactivation of PTV cortex increased F1/F0 ratios of CRF-driven responses of complex cells only. Overall, activation of suppressive surrounds or inactivation of PTV 'converted' substantial proportions (50 and 30%, respectively) of complex cells into simple-like cells (F1/F0 > 1). Thus, the simple-complex distinction depends, at least partly, on information coming from the silent surrounds and/or feedback from 'higher-order' cortices. These results support the idea that simple and complex cells belong to the same basic cortical circuit and the spatial phase-variance of their responses depends on the relative strength of different synaptic inputs.

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PubMed2004

Motion sensitivity in cat's superior colliculus: contribution of different visual processing channels to response properties of collicular neurons.

It is well established that neurons in the retinorecipient layers of superior colliculus (SC), the mammalian homologue of the optic tectum of other vertebrates, are extremely sensitive to moving stimuli. In our studies we have distinguished several functionally distinct groups of neurons in the retinorecipient layers of the SC of the cat on the basis of their velocity response profiles. Our data revealed substantial convergence of the Y and non-Y information channels on single SC neurons. Second, using the method of selective conduction block of the Y-type fibers in one optic nerve we have shown that responses of SC cells to high-velocity motion are dependant on the integrity of Y-type input. Third, in order to determine the degree of influence of the X- and W-type input on cellular responses we have examined spatial and temporal frequency response profiles of single collicular neurons using sinusoidal gratings drifting in the preferred direction. At any given eccentricity, most collicular neurons exhibited a preference for relatively very low spatial frequencies. The preference for low spatial frequencies combined with temporal frequency profiles of collicular neurons suggests that the Y- and W-type inputs constitute the major functional inputs to the retinorecipient layers of the SC and that the "top-down" X-type input from the visual cortex has only a minor impact on the spatio-temporal frequency response profiles of collicular receptive fields.

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PubMedDate not supplied

Spatial coding and response redundancy in parallel visual pathways of the marmoset Callithrix jacchus.

Many neurons in the primary visual cortex (area V1) show pronounced selectivity for the orientation and spatial frequency of visual stimuli, whereas most neurons in subcortical afferent streams show little selectivity for these stimulus attributes. It has been suggested that this transformation is a functional sign of increased coding efficiency, whereby the redundancy (or overlap in response properties) is reduced at consecutive levels of visual processing. Here we compared experimentally the response redundancy in area V1 with that in the three main dorsal thalamic afferent streams, the parvocellular (PC), koniocellular (KC), and magnocellular (MC) divisions of the dorsal lateral geniculate nucleus (LGN) in marmosets. The spatial frequency and orientation tuning of single cells in the LGN and area V1 were measured, using luminance contrast sine-wave gratings. A joint spatial frequency-orientation response selectivity profile was calculated for each cell. Response redundancy for each population was estimated by cross-multiplication of the joint selectivity profiles for pairs of cells. We show that when estimated in this way, redundancy in LGN neurons is approximately double that of neurons in cortical area V1. However, there are differences between LGN subdivisions, such that the KC pathway has a spatial representation that lies between the redundant code of the PC and MC pathways and the more efficient sparse spatial code of area V1.

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