Putative Feed-Forward Control of Jaw-Closing Muscle Activity During Rhythmic Jaw Movements in the Anesthetized Rabbit

Komuro, Akira,Toshifumi Morimoto,Koichi Iwata,Tomio Inoue,Yuji Masuda,Takafumi Kato, andOsamu Hidaka.Putative Feed-Forward Control of Jaw-Closing Muscle ActivityDuring Rhythmic Jaw Movements in the Anesthetized Rabbit. J. Neurophysiol. 86: 2834-2844, 2001. When a thinplastic test strip of various hardness is placed between the upper andlower teeth during rhythmical jaw movements induced by electricalstimulation of the cortical masticatory area (CMA) in anesthetizedrabbits, electromyographic (EMG) activity of the masseter muscle isfacilitated in a hardness-dependent manner. This facilitatorymasseteric response (FMR) often occurred prior to contact of the teethto the strip, and thus preceded the onset of the masticatoryforce. Since this finding suggests involvement of afeed-forward mechanism in the induction of the FMR, the temporalrelationship between the onset of the FMR and that of the masticatoryforce was analyzed in five sequential masticatory cycles afterapplication of the strip. The FMR was found to precede the onset ofmasticatory force from the second masticatory cycle after applicationof the strip, but never did in the first cycle. This finding supportsthe concept of a feed-forward control mechanism that modulates FMRtiming. Furthermore, the FMR preceding the force onset disappearedafter making a lesion of the mesencephalic trigeminal nucleus (MesV)where the ganglion cells of the muscle spindle afferents from thejaw-closing muscles are located. In contrast, no such change occurredafter blocking periodontal afferents by transection of both themaxillary and the inferior alveolar nerves. The putative feed-forwardcontrol of the FMR is therefore dependent mainly on sensory inputs from the muscle spindles, but little on those from the periodontal receptors, if any. We further examined the involvement of the CMA withthe putative feed-forward control of the FMR via the transcorticalloop. For this purpose, rhythmical jaw movements were induced bystimulation of the pyramidal tract. No significant change in the timingof the FMR occurred after the CMA ablation, which strongly suggeststhat the CMA is not involved in the putative feed-forward control ofthe FMR. The FMR was also noted to increase significantly in ahardness-dependent manner even after the MesV lesion, although the rateof increment decreased significantly. Contribution of muscle spindlesand periodontal receptors to the hardness-dependent change of the FMRis discussed.

     

Plasticity of Somatosensory Cortex in Primates

Over recent years, we have come to the surprising realization that sensory cortex is highly plastic in functional organization, even in adult brains. Much of the evidence for this conclusion comes from studies of the effects of peripheral deafferentation or sensory experience on the somatotopy of primary somatosensory cortex (area 3b) of monkeys. Local modifications in cortical representations occur rapidly after sensory loss or more gradually during altered sensory experience. These changes depend on reductions in lateral inhibition and other dynamic adjustments in sensory networks, as well as Hebbian-like modifications of synaptic strengths. Activity-dependent alterations in the expression of neurotransmitters and modulators may also play a role. After major deactivations, such as those produced by amputation or section of dorsal column afferents, cortex regains responsiveness over a much longer time period as a result, at least in part, from the growth of new connections.     

Localization of Somatosensory Evoked Potentials in Primary Somatosensory Cortex: A Comparison Between PCA and MUSIC

The aim of this study was to test source modeling strategies for EEC-data from a clinical group of amputees. The experimental conditions (measuring time, age and condition of the patients) resulted in low quality EEC-data. Noise reduction was achieved by a principal component analysis (PCA) and a multiple signal classification (MUSIC). A comparison of the results of these two methods with traditional signal handling yielded superior results for the MUSIC algorithm.     

Functional Connectivity of the Secondary Somatosensory Cortex of the Rat

The hierarchical relationship of the rat primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) is controversial. The existence of a direct thalamocortical projection from ventral posterolateral thalamic nucleus (VPL) to S2 is a key factor in determining the relative position of S2 in the processing flow. In this study, the inter‐connections of forepaw and hindpaw representations in VPL, S1, and S2 were examined by neuroanatomical tracing and electrophysiological approaches. In the tracing experiments, VPL, S1, and S2 were electrophysiologically identified, and then iontophoretically injected with biotinylated dextran amine (BDA, a bi‐directional tracer). In the double‐labeling experiments, two of the following retrograde tracers—BDA, Rhodamine dextran (RD), and/or Fluoro‐Gold (FG)—were injected into homotypical S1 and S2 forepaw representations simultaneously. In the electrophysiological studies, paired somatic evoked multiunit responses in S1 and S2 were compared. Our results revealed that: (1) VPL forepaw and hindpaw neurons projected to corresponding S1 and S2 areas in a parallel and somatotopic manner; (2) very low percentage of double projecting VPL neurons were found, indicating parallel and independent pathways from forepaw VPL to S1 and S2; (3) forepaw S1 and S2 were symmetrically and reciprocally connected; (4) response latencies of the S1 and S2 multiunits to forepaw stimulation were in accordance with a direct and parallel pathway. This study provides further evidence to support the equivalent hierarchy of S1 and S2 in processing sensory information of the rat. Anat Rec, 291:960–973, 2008. © 2008 Wiley‐Liss, Inc.     

兔皮层体感诱发电位时频特征分析

分析兔皮层体感诱发电位的时域和频域特性。兔麻醉开颅，从大脑体感运动皮层引导诱发电位。连续多次刺激，以3800Hz采样率采样。测量每次诱发电位各个波形成分的峰潜伏期。分析诱发电位的功率谱。比较单次和叠加平均电位的时频特性。结果显示诱发成分时域变异性在一个刺激周期内随时间逐渐增大，诱发电位的频谱包括3个主要频谱包。叠加平均技术使信号产生波形融合，新波形产生，后发放成份消失等多种畸变。     

大鼠体感皮层后爪代表区的微电极测定

利用微电极测绘技术对Wistar大鼠大脑皮层体感一区进行电生理研究,测定了后爪代表区的面积、与相邻代表区的关系。证明后爪代表区内部存在分域关系,但由于后爪皮层代表区神经元的感受野较大,分域是粗略的。     

Computation of Color and Brightness Differences by Rabbit Visual Cortex Neurons

Extracellular recording of the activity of 54 neurons in the rabbit visual cortex in responses to substitutions of eight colored and eight monochromatic stimuli in pairs was studied. Stimuli were uniform flashes of light displayed on an SVGA monitor and illuminated the whole retina. The responses of phasic neurons showed an initial discharge (50–90 msec from the moment of the change in stimulus), associated with the brightness or color difference between the stimuli. These “discrimination discharges” were used to construct an 8 × 8 matrix for each neuron, showing the mean number of spikes per sec in responses to changes in different pairs of stimuli. Processing of the matrix by factor analysis identified the major factors determining the axes of the sensory space. A brightness space with only two dimensions, with darkness and brightness orthogonal axes, was seen for 30% of neurons. A four-dimensional color space was seen in 22% of neurons, with two color and two achromatic axes. The sensory space of these neurons was similar to the spaces obtained by analyzing the early components of visual evoked potentials in rabbits induced by changes in color stimuli and behavioral operant responses in conditioned reflex color differentiation. The fundamental coincidence of the sensory spaces obtained by different methods identifies the general nature of the principle of vector coding and the existence of special neuronal mechanisms for detection of color and brightness differences in the visual field. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 55, No. 1, pp 60–70, January–February, 2005.     

Dynamics of Local Changes and Oscillations in Energy Metabolism in the Rabbit Cerebral Cortex during the Formation of a Conditioned Defensive Reflex

Brain energy metabolism associated with different functional states and different types of human and animal activity is accompanied by dynamic changes in the degree of linkage between glycolysis and oxidative phosphorylation in different cell compartments [20–23, 25]. These processes are reflected in the redox state of brain tissue [27] and can be recorded potentiometrically as changes in the redox state potential (E) of brain tissue [24]. Studies of E in the cortex of rabbits using implanted platinum electrodes showed that during the acquisition of a conditioned defensive reflex using a combination of a light and a mild electric shock to one of the rabbit's ears, cortical E showed oscillations with periods of several seconds after 5–15 combinations. This number of combinations started to be accompanied by generalized changes in E in the cortex, which, at 20–100 combinations, could be either an increase or a decrease in E. As the number of combinations increased, increases in E were gradually replaced by decreases. By 200–400 combinations, oscillations in E disappeared and the episodes of decreased E accompanying combinations acquired a stable local character. These results suggest that there is a change in the balance of the major sources of brain tissue energy supply during the formation and stabilization of a conditioned defensive reflex: at the initial stages of acquisition of the conditioned reflex a number of cortical points have an energy supply dominated by tissue respiration, while the main energy source for brain function during performance of the acquired conditioned defensive reflex is glycolysis.     

Laminar Expression of Ephrin‐A2 in Primary Somatosensory Cortex of Postnatal Rats

Several Eph receptors, prominently EphA4 and EphA7, and their corresponding ligands are known to influence neocortical development, including topographic sorting of thalamocortical axons within primary somatosensory cortex (SI). This study investigated postnatal expression of a ligand that can bind to these receptors, ephrin‐A2. Quantitative methods revealed that expression of ephrin‐A2 mRNA in SI reached maximum levels on postnatal day (P) 4 and dropped thereafter to background by P18. Ephrin‐A2 mRNA expression assessed by in situ hybridization qualitatively revealed a similar time course and localized the expression pattern primarily in two broad laminae in SI, comprising the supragranular and infragranular layers, and with additional expression in the subplate. This expression pattern was investigated in greater detail using immunohistochemistry for ephrin‐A2 protein. Immunoreactivity generally showed the same laminar distribution as seen with in situ hybridization, except that it persisted longer, lasting to approximately P14. Expression in the cortical plate was low or absent within presumptive layer IV, and it remained so as cortical lamination progressed. Double‐labeling immunohistochemistry with confocal microscopy revealed that cortical neurons were the principal elements expressing ephrin‐A2 protein. These findings are consistent with possible involvement of ephrin‐A2, in concert with one or more Eph receptors, in influencing arbor development of thalamocortical axons at cortical layer IV boundaries. Anat Rec, 2012. © 2011 Wiley Periodicals, Inc.