SI neuron response variability is stimulus tuned and NMDA receptor dependent.
ABSTRACT Skin brushing stimuli were used to evoke spike discharge activity in single skin mechanoreceptive afferents (sMRAs) and anterior parietal cortical (SI) neurons of anesthetized monkeys (Macaca fascicularis). In the initial experiments 10-50 presentations of each of 8 different stimulus velocities were delivered to the linear skin path from which maximal spike discharge activity could be evoked. Mean rate of spike firing evoked by each velocity (MFR) was computed for the time period during which spike discharge activity exceeded background, and an across-presentations estimate of mean firing rate (MFR) was generated for each velocity. The magnitude of the trial-by-trial variation in the response (estimated as CV; where CV = standard deviation in MFR/MFR) was determined for each unit at each velocity. MFR for both sMRAs and SI neurons (MFRsMRA and MFRSI, respectively) increased monotonically with velocity over the range 1-100 cm/s. At all velocities the average estimate of intertrial response variation for SI neurons (CVSI) was substantially larger than the corresponding average for sMRAs (CVsMRA). Whereas CVsMRA increased monotonically over the range 1-100 cm/s, CVSI decreased progressively with velocity over the range 1-10 cm/s, and then increased with velocity over the range 10-100 cm/s. The position of the skin brushing stimulus in the receptive field (RF) was varied in the second series of experiments. It was found that the magnitude of CVSI varied systematically with stimulus position in the RF: that is, CVSI was lowest for a particular velocity and direction of stimulus motion when the skin brushing stimulus traversed the RF center, and CVSI increased progressively as the distance between the stimulus path and the RF center increased. In the third series of experiments, either phencylidine (PCP; 100-500 microg/kg) or ketamine (KET; 0.5-7.5 mg/kg) was administered intravenously (iv) to assess the effect of block of N-methyl-D-aspartate (NMDA) receptors on SI neuron intertrial response variation. The effects of PCP on both CVSI and MFRSI were transient, typically with full recovery occurring in 1-2 h after drug injection. The effects of KET on CVSI and MFRSI were similar to those of PCP, but were shorter in duration (15-30 min). PCP and KET administration consistently was accompanied by a reduction of CVSI. The magnitude of the reduction of CVSI by PCP or KET was associated with the magnitude of CVSI before drug administration: that is, the larger the predrug CVSI, the larger the reduction in CVSI caused by PCP or KET. PCP and KET exerted variable effects on SI neuron mean firing rate that could differ greatly from one neuron to the next. The results are interpreted to indicate that SI neuron intertrial response variation is 1) stimulus tuned (intertrial response variation is lowest when the skin stimulus moves at 10 cm/s and traverses the neuron's RF center) and 2) NMDA receptor dependent (intertrial response variation is least when NMDA receptor activity contributes minimally to the response, and increases as the contribution of NMDA receptors to the response increases).
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ABSTRACT: Neural representation of somatosensory events undergoes major transformation in the primary somatosensory cortex (SI) from its original, more or less isomorphic, form found at the level of peripheral receptors. A large body of SI optical imaging, neural recording and psychophysical studies suggests that SI representation of stimuli encountered in everyday life is a product of dynamic processes that involve competitive interactions at multiple levels of cortical organization. Such interactions take place among neighboring neurons, among local groups of minicolumns, among neighboring macrocolumns, between SI and SII, between Pacinian and non-Pacinian channels, and bilaterally between homotopic somatosensory regions of the opposite hemispheres. Together these interactions sharpen SI response to suprathreshold and time-extended tactile stimuli by funneling the initially widespread stimulus-triggered activity in SI into the local group of macrocolumns most directly driven by the stimulus. Those macrocolumns in turn fractionate into stimulus-specific patterns of differentially active minicolumns. Thus SI dynamically shapes its representation of a tactile stimulus by selecting among all of its neurons initially activated by the stimulus a subset of neurons with receptive-field and feature-tuning properties closely matching those of the stimulus. Through this stimulus-directed dynamical selection process, which operates on a scale of hundreds of milliseconds, SI achieves a more faithful representation of stimulus properties, which is reflected in improved performance on tactile perceptual tasks.Neuroscience & Biobehavioral Reviews 10/2009; 34(2):160-70. DOI:10.1016/j.neubiorev.2009.08.009 · 10.28 Impact Factor
Conference Paper: Principles of minimal control for comprehensive team behaviour[Show abstract] [Hide abstract]
ABSTRACT: We present an approach to the design of a comprehensive set of behaviours for locally-controlled robots which must engage in inter-group competition. Such a “comprehensive” set of behaviours includes the ability to make progress towards team goals and obstruct progress of opponents by interacting constructively with teammates, and safely with all environmental objects. Our design principles guide us to maintain complexity of desired behaviour while minimizing complexity of control and requirements of accurate sensing, precise action, and communication. The resulting systems are small, simple, robust, and easily portable between platforms. These methods are discussed in the context of the design of the “Spirit of Bolivia”, a soccer team of five autonomous robots which was undefeated in the RoboCup '97 championship, and which is currently training for RoboCup '98Robotics and Automation, 1998. Proceedings. 1998 IEEE International Conference on; 06/1998