Biomedical subjects

Keisuke Kawasaki

Publications and source records attributed to Keisuke Kawasaki.

4 recordsLinked to original sources

PubMed2006

Initial saccades predict manual recognition choices in the monkey.

In animals with specialized foveae, eye position has a direct influence over the acquisition of detailed visual information. At the same time, eye movements executed during natural behaviors are closely linked with motor actions. In this study, we investigated patterns of eye movements during a simple visual discrimination task. Three rhesus monkeys learned to recognize images of real world objects with no explicit constraints on eye position. Analysis of the monkeys' eye movements showed that although the endpoint of the initial saccade depended on the particular visual stimulus, the trajectory of the first saccades also reliably predicted the manual response associated with that stimulus. We thus observed that initial saccades executed in a recognition task reflect both perceptual and motor aspects of a visual task. This pattern of eye movements emerged spontaneously in all three animals tested despite the fact that saccades were never explicitly rewarded. As the average saccade latency was under 200ms, object specific learned associations must have exerted their influence over the initial saccade even earlier, providing a novel temporal marker for the rapidity of visual recognition processes. Taken together, these results suggest that caution should be exercised when interpreting the meaning of oculomotor patterns observed during perceptual tasks, as these blur the line between perceptual processing and motor preparation.

Animals↗

PubMed2006

Effects of long-term object familiarity on event-related potentials in the monkey.

Although some change in the neural representation of an object must occur as it becomes familiar, the nature of this change is not fully understood. In humans, it has been shown that the N170-an evoked visual potential-is enhanced for classes of objects for which people have visual expertise. In this study, we explored whether monkeys show a similar modulation in event-related potential (ERP) amplitude as a result of long-term familiarity by recording ERPs with chronically implanted electrodes over extended training periods spanning many sessions. In each of 3 experiments, we found larger amplitude visual evoked responses to highly familiar images for the time period of 120-250 ms after stimulus onset. This difference was found when the monkeys were trained in an individual-level discrimination task, in a task that required only color discrimination, and even following a viewing-only task. We thus observed this familiarity effect across several tasks and different object categories and further found that the difference between "familiar" and "novel" became smaller as the animals gained experience with the previously unfamiliar objects across multiple test sessions. These data suggest that changes in visual responses associated with familiarity are evident early in the evoked visual response, are robust, and may be automatic, driven at least in part by repeated object exposure.

Animals↗

PubMed2004

Presumed inhibitory neurons in the macaque inferior temporal cortex: visual response properties and functional interactions with adjacent neurons.

Neurons in area TE of the monkey inferior temporal cortex respond selectively to images of particular objects or their characteristic visual features. The mechanism of generation of the stimulus selectivity, however, is largely unknown. This study addresses the role of inhibitory TE neurons in this process by examining their visual response properties and interactions with adjacent target neurons. We applied cross-correlation analysis to spike trains simultaneously recorded from pairs of adjacent neurons in anesthetized macaques. Neurons whose activity preceded a decrease in activity from their partner were presumed to be inhibitory neurons. Excitatory neurons were also identified as the source neuron of excitatory linkage as evidenced by a sharp peak displaced from the 0-ms bin in cross-correlograms. Most inhibitory neurons responded to a variety of visual stimuli in our stimulus set, which consisted of several dozen geometrical figures and photographs of objects, with a clear stimulus preference. On average, 10% of the stimuli increased firing rates of the inhibitory neurons. Both excitatory and inhibitory neurons exhibited a similar degree of stimulus selectivity. Although inhibitory neurons occasionally shared the most preferred stimuli with their target neurons, overall stimulus preferences were less similar between adjacent neurons with inhibitory linkages than adjacent neurons with common inputs and/or excitatory linkages. These results suggest that inhibitory neurons in area TE are activated selectively and exert stimulus-specific inhibition on adjacent neurons, contributing to shaping of stimulus selectivity of TE neurons.

Action Potentials↗

PubMed2004

Hoechst 33342 is a useful cell tracer for a long-term investigation of articular cartilage repair.

The repair process of a full-thickness osteochondral defect was observed in a rat model using Hoechst 33342 as a cell tracer. The osteochondral defect was created at the medial femoral condyle of the right knee joints of twelve 11 week old male rats. Three weeks after the surgery, Hoechst 33342 was injected into the same knee joints. Calcein, a marker of the mineralization front, was then injected subcutaneousely twice at seven days and one day before harvesting of the tissue. At six, ten, and fourteen weeks and one year after the surgery, femoral condyles were obtained from the operated knee joints, fixed by alcohol, and embedded in polymethylmethacrylate. The sections were examined by fluorescent and then light microscopy. In the lateral femoral condyle cartilage, Hoechst 33342 labeling of chondrocyte nuclei was observed in all layers of the intact cartilage, and the dye never infiltrated beneath the subchondral bone plate. At 6 weeks after the surgery, Hoechst 33342-positive cells were observed not only in the regenerated fibrous cartilage, but also in the newly formed mineralized tissue in the medial femoral condyle. Interestingly, Hoechst 33342 labeling remained undiminished even one year after the intra-articular injection. The findings of the present study suggest that intra-articular injection of Hoechst 33342 is a useful tracer for long-term investigations of chondrocyte differentiation in vivo.

Animals↗