Biomedical subjects

Takuji Kasamatsu

Publications and source records attributed to Takuji Kasamatsu.

3 recordsLinked to original sources

PubMed2006

Contrast-dependent, contextual response modulation in primary visual cortex and lateral geniculate nucleus of the cat.

In the primary visual cortex (V1), the responses of neurons to stimuli presented in their classical receptive fields (CRFs) are modulated by another stimulus concurrently presented in their surround (receptive field surround, SRF). We studied the nature of the modulatory effects of SRF stimulation with respect to stimulus contrast in cat V1. In 51 V1 neurons studied, large SRF stimuli (40 degreesx30 degrees ) induced only the suppression of responses to CRF stimulation and the suppressive effects became stronger as the contrast for SRF stimulation increased. The contrast sensitivity of SRF suppression did not correlate with that of CRF responses. By independently controlling contrast of CRF and SRF stimuli, we studied whether SRF effects vary with CRF response magnitude. Increasing contrast for CRF stimulation caused an upward shift of the range of effective contrasts for SRF stimulation, indicating that a high contrast for SRF stimulation is required for suppressing strong responses to CRF stimulation at high contrasts. To assess the possible origin of the suppressive SRF effect on V1 neurons, we also investigated the contrast dependency of SRF effects in 28 neurons from the lateral geniculate nucleus. Our results suggest that SRF effects obtained at the subcortical level strongly contribute to those in V1. Taken together, we conclude that along the thalamocortical projections, SRF modulation exhibits a gain-control mechanism that scales the suppressive SRF effect depending on the contrast for CRF stimulation. In addition, SRF effects can be facilitatory at low stimulus contrasts potentially due to the enlargement of the summation field.

Algorithms↗

PubMed2002

Artifactual synchrony via capacitance coupling in multi-electrode recording from cat striate cortex.

Elucidation of neural connectivity patterns in the brain are thought to give us a mechanistic understanding of how the brain works. Functional connectivity is best studied by simultaneous recording of single-unit activity from many neurons. Accordingly, various types of multiple-microelectrode systems have been developed. We have studied long-range lateral interactions in cat striate cortex. To physiologically characterize interacting cells recorded simultaneously, we used two microelectrodes whose movements were controlled by two independently-movable microdrives. The tips of the two microelectrodes were separated by approximately 2 mm or more. During preliminary plotting of two receptive fields of cell pairs, we often noted the emergence of perfectly synchronous firing between two spike trains (amplitude ratio, about 20:1) registered with two microelectrodes. Synchronously firing, smaller spikes disappeared when larger spikes of the pair were lost to either substantial advancement of or placing an electrolytic lesion at the electrode registering the latter. The synchrony also disappeared when two microdrive systems were shielded individually. We concluded that the synchrony was attained through capacitance coupling between two microdrive systems. We proposed a few practical recommendations to avoid the contamination of cross correlograms with the false-positive, narrow peak at time zero due to the presence of reflected spike trains.

Action Potentials↗

PubMedDate not supplied

Muscimol and baclofen differentially suppress retinotopic and nonretinotopic responses in visual cortex.

This study relates to local field potentials and single-unit responses in cat visual cortex elicited by contrast reversal of bar gratings that were presented in single, double, or multiple discrete patch (es) of the visual field. Concurrent stimulation of many patches by means of the pseudorandom, binary m-sequence technique revealed interactions between their respective responses. An analysis identified two distinct components of local field potentials: a fast local component (FLC) and a slow distributed component (SDC). The FLC is thought to be a primarily postsynaptic response, as judged by its relatively short latency. It is directly generated by thalamocortical volleys following retinotopic stimulation of receptive fields of a small cluster of single cells, combined with responses to recurrent excitation and inhibition derived from the cells under study and immediately neighboring cells. In contrast, the SDC is thought to be an aggregate of dendritic potentials related to the long-range lateral connections (i.e. long-range coupling). We compared the suppressive effects of a GABA(A)-receptor agonist, muscimol, on the FLC and SDC with those of a GABA(B)-receptor agonist, baclofen, and found that muscimol more strongly suppressed the FLC than the SDC, and that the reverse was the case for baclofen. The differential suppression of the FLC and SDC found in the present study is consistent with the notion that intracortical electrical signals related to the FLC terminate on the somata and proximal/basal dendrites, while those related to the SDC terminate on distal dendrites.

Animals↗