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M Shidara

Publications and source records attributed to M Shidara.

At least 19 recordsLinked to original sources
PubMed1998

Neuronal signals in the monkey ventral striatum related to progress through a predictable series of trials.

Single neurons in the ventral striatum of primates carry signals that are related to reward and motivation. When monkeys performed a task requiring one to three bar release trials to be completed successfully before a reward was given, they seemed more motivated as the rewarded trials approached; they responded more quickly and accurately. When the monkeys were cued as to the progress of the schedule, 89 out of 150 ventral striatal neurons responded in at least one part of the task: (1) at the onset of the visual cue, (2) near the time of bar release, and/or (3) near the time of reward delivery. When the cue signaled progress through the schedule, the neuronal activity was related to the progress through the schedule. For example, one large group of these neurons responded in the first trial of every schedule, another large group responded in trials other than the first of a schedule, and a third large group responded in the first trial of schedules longer than one. Thus, these neurons coded the state of the cue, i.e., the neurons carried the information about how the monkey was progressing through the task. The differential activity disappeared on the first trial after randomizing the relation of the cue to the schedule. Considering the anatomical loop structure that includes ventral striatum and prefrontal cortex, we suggest that the ventral striatum might be part of a circuit that supports keeping track of progress through learned behavioral sequences that, when successfully completed, lead to reward.

Action Potentials↗
PubMed1998

Temporal firing patterns of Purkinje cells in the cerebellar ventral paraflocculus during ocular following responses in monkeys I. Simple spikes.

The simple-spike firing frequency of 30 Purkinje cells (P cells) in the ventral paraflocculus (VPFL) of alert monkeys was studied in relation to vertical slow eye movements, termed ocular following response (OFR), induced by large-field visual motions of different velocities and durations. To quantitatively analyze the relationship between eye movement and firing frequency, an inverse dynamics representation of the eye movement was used for reconstructing the temporal waveform of firing. Coefficients of eye-acceleration, velocity, and position, bias, and time lag between firing and eye movement were estimated by least-square error method. In the regression analyses for each stimulus condition, 86% (146/170) of the well-modulated temporal firing patterns taken from those 30 P cells were reconstructed successfully from eye movement. The model with acceleration, velocity, and position terms, which we used, was shown as the best among several potential models by Cp statistics, consistent with t-test of significance of each term. Reliable coefficients were obtained from 75% (109/146) of the well-reconstructed firing patterns of 28 cells among 30. The estimated coefficients were larger (statistically significant) for slow stimuli than for fast stimuli, suggesting changes in sensitivities under different conditions. However, firing patterns of each cell under several different conditions were frequently well reconstructed by an inverse dynamics representation with a single set of coefficients (13 cells among 21). This indicates that the relationships between P cell firing and OFR are roughly linear in those stimulus ranges. The estimated coefficients for acceleration and velocity suggested that the VPFL P cells properly encode the dynamic components of the motor command during vertical OFR. As for the positional component, however, these P cells are correlated with eye movement in the opposite direction. In the regression analysis without positional component, remarkable differences between observed and reconstructed firing patterns were noted especially in the initial phase of the movements, indicating that the negative positional component was not negligible during OFR. Thus we conclude that, during OFR, the VPFL P cells cannot provide the necessary final motor command, and other brain regions, downstream neural structures, or other types of P cells must provide lacking position-dependent motor commands. This finding about the negative correlation with the position is in the opposite sign with previous studies obtained from the fixation and the smooth pursuit movement. From these comparisons, how the VPFL contributes to a part of the final motor command or how other brain regions complement the VPFL is suggested to be different for early and late phases of the movements.

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PubMed1994

Information representation by Purkinje cells in the cerebellum during ocular following responses.

A quantitative analysis of simple spike activity of Purkinje cells (P-cells) in the cerebellum of awake monkeys suggested their possible contribution in motor control. Simple spike activities of ventral parafloccular P-cells were recorded during short-latency ocular following responses. The relationship between the firing frequency of these P-cells and the simultaneously recorded eye movements during ocular following was analyzed by using a linear time-series regression method. The result suggests that ventral parafloccular P-cells contribute to the dynamic (velocity and acceleration) rather than the static (position) control of eye movements.

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PubMed1994

Neural activity in cortical area MST of alert monkey during ocular following responses.

1. We studied response properties of neurons in the superior temporal sulcus (STS) of behaving monkeys that discharged during brief, sudden movements of a large-field visual stimulus, eliciting ocular following. Most neurons responded to movements of a large-field visual stimulus with directional selectivity, preferring high stimulus speeds. Neurons were mostly recorded in the medial superior temporal area (MST) (187/250) and the middle temporal area (MT) (57/250). Further response properties were studied in the MST neurons. 2. Response latencies were measured when a large-field random dot pattern was moved in the preferred direction and preferred speed for each neuron. Eighty percent (120/150) of the neurons were activated < 50 ms after the onset of the stimulus motion. In most cases (89%, 134/150), increased firing rates started before the eye movements, with 59% (88/150) starting > 10 ms before the eye movements. 3. The relationship between the latency of neuronal responses and that of eye movements was studied in 59 neurons by changing the stimulus speed systematically (10-160 degrees/s). The latencies of both neuronal and ocular responses decreased as stimulus speed increased. As a result, the time difference between the response latencies for neuronal and ocular responses varied little with changes in stimulus speed. 4. Blurring of the random dot pattern, by interposing a sheet of ground glass, increased the latency of both neuronal responses and eye movements. 5. With the use of a check pattern instead of random dots, both neuronal and ocular responses began to decrease rapidly when the temporal frequency of the visual stimulus exceeded 20 Hz. At 40 Hz the neurons showed a distinctive burst-and-pause firing pattern, and the eye movements showed signs of oscillation. 6. The response properties of the MST neurons during ocular following were similar to those of the dorsolateral pontine nucleus (DLPN) neurons, reported previously. Our results indicate that the MST neurons may provide visual information to the DLPN neurons and may play a role in eliciting ocular following. 7. Responses during smooth-pursuit eye movement were studied in 55 MST neurons. Each of these neurons responded to the moving large-field visual stimulus, which elicited ocular following, and 40 of these neurons were activated during smooth pursuit in the dark. Response latencies during smooth pursuit were long in those neurons having different directional preferences during smooth pursuit and ocular following but were short for those having the same directional preferences during smooth pursuit and ocular following.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1993

Inverse-dynamics model eye movement control by Purkinje cells in the cerebellum.

Many lines of evidence suggest that the cerebellum is involved in motor control. But what features of these movements are encoded by cerebellar neurons? For slow-tracking eye movements, the activity of Purkinje cells in the ventral paraflocculus of the cerebellum is known to be correlated with eye velocity and acceleration. Here we show that the complex temporal pattern of the firing frequency that occurs during the ocular following response elicited by movements of a large visual scene can be reconstructed by an inverse-dynamics representation, which uses the position, velocity and acceleration of eye movements. Further analysis reveals that the velocity and acceleration components can provide appropriate dynamic drive signals to ocular motor neurons, whereas the position component often has the wrong polarity. We conclude that these Purkinje cells primarily contribute dynamic command signals.

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PubMed1993

Role of Purkinje cells in the ventral paraflocculus in short-latency ocular following responses.

We describe the simple-spike activity of Purkinje cells (P cells) in the ventral paraflocculus (VPFL) of behaving monkeys in association with movements of the visual scene that evoke short-latency ocular following responses. One group of P cells discharged maximally for downward motion, and the other for motion toward the side of the recording. The onset of the simple-spike response was measured in relation to the onset of ocular following in 24 P cells. The majority of P cells (79%) led by 1-9 ms. At the site of each recording, electrical stimuli (single negative pulses, 1.5-45 microA; 0.2 ms in width) were applied and 60% (18/30) of the sites elicited eye movements in the preferred direction of the P cells. The latency of the single-pulse-evoked response in the ipsilateral eye ranged from 8.6 to 10.9 ms. These data suggest that the P cells in the VPFL play a role in ocular following; some discharge early enough to generate the very earliest eye movements.

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PubMed1992

Neural activity in dorsolateral pontine nucleus of alert monkey during ocular following responses.

1. Movements of the visual scene evoke short-latency ocular following responses. To study the neural mediation of the ocular following responses, we investigated neurons in the dorsolateral pontine nucleus (DLPN) of behaving monkeys. The neurons discharged during brief, sudden movements of a large-field visual stimulus, eliciting ocular following. Most of them (100/112) responded to movements of a large-field visual stimulus with directional selectivity. 2. Response amplitude was measured in two components of the neural response: an initial transient component and a late sustained component. Most direction-selective DLPN neurons showed their strongest responses at high stimulus speeds (80-160 degrees/s), whether their response components were initial (63/87, 72%) or sustained (63/87, 72%). The average firing rates of 87 DLPN neurons increased as a linear function of the logarithm of stimulus speed up to 40 degrees/s for both initial and sustained responses. 3. Not only the magnitude but also the latency of the neural and ocular responses were dependent on stimulus speed. The latencies of both neural and ocular responses were inversely related to the stimulus speed. As a result, the time difference between the response latencies for neural and ocular responses did not vary much with changes of stimulus speed. 4. Response latency was measured when a large-field random dot pattern was moved in the preferred direction and at the preferred speed of each neuron. Seventy-three percent (56/77) of the neurons were activated less than 50 ms after the onset of the stimulus motion. In most cases (67/77, 87%), their increase of firing rate started before the eye movements, and 34% of them (26/77) started greater than 10 ms before the eye movements. 5. Blurring of the random dot pattern by interposing a sheet of ground glass increased the latency of both neural responses and eye movements. On the other hand, the blurred images did not change the timing of the effect of blanking the visual scene on the responses of the neurons or eye movements. 6. When a check pattern was used instead of random dots, both neural and ocular responses began to decrease rapidly when the temporal frequency of the visual stimulus exceeded 20 Hz. When the temporal frequency of the visual stimulus approached 40 Hz, the neurons showed a distinctive burst-and-pause firing pattern. The eye movements recorded at the same time showed signs of oscillation, and their temporal patterns were closely correlated to those of the firing rate.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1991

Developmental changes in delayed rectifier K+ currents in the muscular- and neural-type blastomere of ascidian embryos.

1. Developmental changes in the amplitude, kinetic properties, tetraethyl-ammonium (TEA) sensitivity, and ion selectivity of the delayed rectifier K+ currents were investigated in differentiating muscular-type (M) and neural-type (N) blastomeres isolated from the early cleavage-arrested ascidian embryos, using conventional two-microelectrode voltage clamp techniques. 2. No voltage-sensitive outward K+ currents were found in either type of blastomere during the first 35 h of development at 9 degrees C. Thereafter the delayed rectifier K+ current became apparent. The peak amplitude of the K+ current in the M-blastomere increased abruptly from 50 to 60 h and tended to plateau after 60 h, while in the N-blastomere it continued to increase after initial emergence at around 35 h. 3. The threshold potential level of the K+ current in the M-blastomere was initially about -10 mV in a standard external solution (1 mM-K+ solution), but shifted towards the hyperpolarized direction until it reached a steady level at 45 h after fertilization. At the fully differentiated stages, the threshold was around -32 mV and -26 mV in the M- and N-blastomeres, respectively. 4. Throughout development, the reversal potential of the tail current changed with the external K+ concentration in both M- and N-blastomeres as expected for a K(+)-electrode. There was no significant difference in the selectivity ratios for the K+ channel between the two types of blastomeres. The relative selectivities were K+ (1.000): Rb+ (0.774): NH4+ (0.122): Na+ (0.074) and K+ (1.000): Rb+ (0.724): NH4+ (0.155): Na+ (0.074) in the M- and N-blastomeres, respectively. 5. Modified Scatchard plots of TEA-sensitivity data indicated a one-to-one reaction between TEA and the K+ channel. These plots revealed the presence of TEA-resistant K+ channels in addition to TEA-sensitive K+ channels in the M-blastomere, but revealed only TEA-sensitive K+ channels in the N-blastomere. The dissociation constant (Ki) values of these three types of K+ channel did not change during development. In the M-blastomere, the Ki of the TEA-sensitive K+ channel was 1.29 +/- 0.05 mM (mean +/- S.E.M., n = 31) and that of the TEA-resistant K+ channel was 1.4 +/- 0.1 M (mean +/- S.E.M., n = 31) at a test potential of 45 mV. The Ki value of the neural-type K+ current was 1.38 +/- 0.03 mM (mean +/- S.E.M., n = 20) at 45 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1990

Changes in sodium channels during neural differentiation in the isolated blastomere of the ascidian embryo.

1. The current density and the kinetics of voltage-sensitive sodium channels during neural differentiation were examined in the isolated, cleavage-arrested blastomere of ascidian embryos which contains presumptive neural regions. The macroscopic sodium current were measured with the two-microelectrode voltage-clamp technique and the single sodium channel currents were recorded with the patch-clamp technique under the cell-attached configuration. 2. The entire time course of sodium channel development could be divided into three phases from the current density and channel gating properties. 3. In the first phase, from fertilization to about 40 h, the density of the sodium channel current was from 8 to 50 microA cm-2. The channel gating properties were similar to those of the sodium channel in the egg cell except for a negative shift in the voltage dependence of the peak inward current, the steady-state inactivation, and the decay time constant. The sodium channels in this phase were classified as 'type-I' channels. 4. In the second phase (40-60 h after fertilization), the density of the sodium channel current increased from 20 to 800 microA cm-2. The curves of the I-V relationship and of the steady-state inactivation shifted in the positive direction by 5-10 mV. 5. At 45-55 h, when the rate of increase in the sodium current was greatest, as much as 40 microA cm-2 h-1, the decay time course of the sodium current became slowest. The time for the current to decline from the peak to the one-tenth of the peak (t 1/10) increased to about five times that in the first phase. After 55 h t 1/10 gradually decreased. 6. In this phase, steady-state inactivation curves showed two inflexion points at different levels of membrane potential and were fitted with a sum of two Boltzmann distribution curves with distinct parameters. The relative contribution of the component with its voltage dependence shifted in the positive direction tended to decrease with development. 7. On examining single-channel recordings, two types of sodium channel were identified in this phase. One type (type-II) showed frequent repetitions of open-to-shut states throughout a voltage step. The ensemble current of the type-II channel showed a slow decay, suggesting that this type of channel may underlie the markedly slow decay of the macroscopic current in this phase. The second type (type-III) had more late openings than the type-I channel but fewer than the type-II channel.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1990

Inactivation kinetics of the sodium channel in the egg and the isolated, neurally differentiated blastomere of the ascidian.

1. Inactivation kinetics of the sodium channel was compared between the egg-type channel in the egg cell and the differentiated-type channel in the cleavage-arrested, neurally differentiated blastomere of the ascidian. The techniques of the two-microelectrode voltage clamp and the cell-attached patch clamp were used. 2. In both types of channel, the time course of inactivation development obtained with a two-pulse protocol at potentials from -40 to -60 mV could be fitted with two exponentials with distinctive parameters. 3. The time course of recovery from inactivation at potentials more negative than -70 mV was compared between the two types of channel. At -80 to -120 mV, a delay of recovery was evident in the egg-type channel, whereas no delay was observed in the differentiated type. 4. In both types of channel, the two time constants of the inactivation of the macroscopic current, derived from the measurements of inward current, inactivation development and recovery from inactivation, had a bell-shaped voltage dependency. The fast time constants had a peak at -55 mV in the differentiated type and -70 mV in the egg type. The slow time constants had a peak around -60 mV in both types. 5. At the single-channel level, the averaged current from the differentiated-type channel showed both fast and slow decays. The frequency of late openings was higher in the differentiated-type channel than in the egg type. 6. The voltage dependence of the decay time constant and the carried charge in the summed current of the single-channel events was found to be shifted in the negative direction by 10-30 mV, compared with that of the macroscopic current. 7. The possibility that the higher frequency of late openings in the differentiated-type channel might be derived from delayed activation was excluded, since first-latency histograms of the single channel were not significantly different between the two types of channel.

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PubMed1987

Kinetic differences between Na channels in the egg and in the neurally differentiated blastomere in the tunicate.

In the tunicate embryo, the cleavage can be arrested at any stage by treatment with cytochalasin B, and yet treated blastomeres can express differentiated phenotypes after a certain period of incubation. We took advantage of these large differentiated blastomeres, which were amenable to electrophysiological recordings, to compare Na channels in the egg cell and those in the neurally differentiated blastomere. The macroscopic Na current in the differentiated blastomere showed a marked slow-decaying component in addition to a fast one, whereas in the egg the fast-decaying component was predominant. Both the I-V relationship and the steady-state inactivation curve shifted about 8 mV in the positive direction in the neurally differentiated blastomere compared with those in the egg cell. Furthermore, single-channel current recordings revealed that Na channels reopened more frequently in the differentiated blastomere than in the egg cell. This characteristic of the channel corresponded well to the marked slow-decaying component of the macroscopic current in the differentiated blastomere. The single-channel conductance was similar in both types of cells. We conclude that the neurally differentiated blastomere expresses a Na channel that has properties of inactivation kinetics distinct from those of the egg-type Na channel and that no detectable egg-type channel coexists in the neurally differentiated blastomeres.

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