The medial frontal cortex and gastric motility: Microstimulation results and their possible significance for the overall pattern of organization of rat frontal and parietal cortex

Bilateral intracortical microstimulation (60–90 s trains of 0.5 ms pulses at 10 Hz, currents below 50 μA) of medial frontal infralimbic and prelimbic cortical areas in ketamine-anesthetized rats produces clear and consistent decreases in ongoing gastric motility. The majority of responses consists of reductions in gastric tone, reductions in the amplitude of gastric contractions, or combined reductions in tone and amplitude. Bilateral section of the vagus nerves eliminates most of the responses, suggesting that the responses are mediated by this nerve. The effective corticdal stimulation zone (the ‘visceral motor’ cortex) largely overlaps the source of the recently described direct projection from medial frontal cortex to the nucleus of the solitary tract; this pathway may be involved in producing the effect. Connections of this cortex with the limbic system suggest it may be involved in producing physiological responses to stress. The topographical, medial to lateral sequence of cortical functional areas revealed by these and other experiments (visceral motor, frontal eye fields, somatic motor, somatic sensory, visceral sensory) is discussed, as well as the possible implications of this pattern to the question of cortical evolutionary development.     

猕猴躯体感觉I区与运动区皮层内微刺激对外周皮肤痛阈的影响

采用慢性微电极实验方法，在５只清醒猕猴上观察了躯体感觉Ｉ区（ＳＩ）与躯体运动区（ＭＳＩ）皮层内微刺激对外周皮肤痛阈的影响。结果①在６８次ＳＩ区皮层内刺激实验中有６７次引起对侧相应皮肤感受野痛阈的变化，其中５２次痛阈升高；分别刺激左右两侧ＳＩ区皮层痛阈变化无明显差异。在不同深度刺激皮层，浅层（０．５ｍｍ）和深层（２．５ｍｍ）痛阈升高明显，中层（１．５ｍｍ）无明显改变。用不同强度刺激皮层，在左ＳＩ区０．４和０．８μＡ引起痛阈明显升高。②在ＭＳＩ区进行４７次皮层内刺激实验，全部引起对侧相应皮肤感受野痛阈变化，其中３０次痛阈升高；分别刺激左右ＭＳＩ区，痛阈改变程度不同。在浅层和深层刺激皮层，痛阈升高更明显。用不同强度分别刺激左右ＭＳＩ区，痛阈改变亦有差异，而以１．２μＡ刺激左ＭＳＩ区皮层痛阈升高最为明显。提示ＳＩ和ＭＳＩ区可能都参与了痛觉的产生和调制作用。     

Projection of the digit and wrist area of precentral gyrus to the putamen: Relation between topography and physiological properties of neurons in the putamen

The autoradiographic technique was used to examine the projection from the digit and wrist area of the precentral gyrus to the putamen in two macaque monkeys. Motor responses elicited by intracortical microstimulation were mapped to guide selection of the site of injection of isotope. Additionally, an electrophysiological study of the activity of putamen neurons during voluntary movements of the distal arm in an awake monkey was performed prior to the anatomical study in one of the animals. Two major findings resulted from this study. Firstly, the area of representation of the digits and wrist in area 4 gives rise to a substantial projection to the putamen. The distribution of terminals consisted of a simple pattern of clusters at anterior levels of the putamen. At caudal levels in the putamen, the clusters merged into a single diagonal band of label. This basic pattern was found to be virtually identical in the two monkeys. Secondly, the location of neurons in the putamen which were activated during voluntary movements of the distal arm was closely associated with the terminal distribution of fibers from the digit and wrist zone of area 4. These data provide strong evidence to support the idea that the putamen is concerned with motor function of distal muscles of the arm, and that the topographic characteristics of the corticoputamen projection are closely related to the physiological properties of individual neurons in the putamen.     

Movements of the jaw and orofacial regions evoked by stimulation of two different cortical areas in cats

Functional properties of the jaw and orofacial motor areas in the cerebral cortex of the lightly anesthetized cat were studied on the basis of the motor effects produced by intracortical microstimulation (ICMS). Jaw and orofacial motor effects were evoked by ICMS (less than 30 microA) delivered to the anterior parts of the coronal and lateral sigmoid gyri (C, coronal area), and the anterior part of the orbital gyrus (O, orbital area). Different patterns of movements in the jaw and orofacial regions were evoked from these two areas. In C one or, at most, two types of simple movement were produced by ICMS to one location, while in O more coordinated movements than those in C were produced. Cytoarchitectonically the jaw and orofacial motor areas were restricted to areas 3a, 4 gamma, and 6a beta in C, and to area 43 in O.     

Distribution and response characteristics of masseteric nerve-driven neurons in two separate cortical projection areas of cats

Cortical projection areas and distribution and response characteristics of masseteric nerve-driven neurons (MDN) were studied by recording surface-evoked potentials and single neuronal activities elicited by stimulation of the contralateral masseteric nerve in cats. Neuronal activities of MDNs could be recorded in two separate cortical areas. One was located in laminae II-III of area 3b of the posterior part of the coronal gyrus (P), and the other in laminae IV-V of areas 3a and 6a beta of the anterior parts of the coronal and lateral sigmoid gyri (A). The majority of MDNs were driven by low-threshold muscle afferents (Group I and II). Peak latencies of MDNs in P were shorter than those in A. Intracortical microstimulation (less than 30 microA) in A produced oro-facial movements while stimulation in P did not produce any motor effects.     

The relationship of corpus callosum connections to electrical stimulation maps of motor, supplementary motor, and the frontal eye fields in owl monkeys

Microstimulation and anatomical techniques were combined to reveal the organization and interhemispheric connections of motor cortex in owl monkeys. Movements of body parts were elicited with low levels of electrical stimulation delivered with microelectrodes over a large region of precentral cortex. Movements were produced from three physiologically defined cortical regions. The largest region, the primary motor field, M-I, occupied a 4-6-mm strip of cortex immediately rostral to area 3a. M-I represented body movements from tail to mouth in a grossly somatotopic mediolateral cortical sequence. Specific movements were usually represented at more than one location, and often at as many as six or seven separate locations within M-I. Although movements related to adjoining joints typically were elicited from adjacent cortical sites, movements of nonadjacent joints also were produced by stimulation of adjacent sites. Thus, both sites producing wrist movements and sites producing shoulder movements were found next to sites producing digit movements. Movements of digits of the forepaw were evoked at several locations including a location rostral to or within cortex representing the face. Overall, the somatotopic organization did not completely correspond to previous concepts of M-I in that it was neither a single topographic representation, nor two serial or mirror symmetric representations, nor a "nesting about joints" representation. Instead, M-I is more adequately described as a mosaic of regions, each representing movements of a restricted part of the body, with multiple representations of movements that tend to be somatotopically related. A second pattern of representation of body movements, the supplementary motor area (SMA), adjoined the rostromedial border of M-I. SMA represented the body from tail to face in a caudorostral cortical sequence, with the most rostral portion related to eye movements. Movements elicited by near-threshold levels of current were often restricted to a single muscle or joint, as in M-I, and the same movement was sometimes multiply represented. Typically, more intense stimulating currents were required for evoking movements in SMA than in M-I. A third motor region, the frontal eye field (FEF), bordered the representation of eyelids and face in M-I. Eye movements elicited from this cortex consisted of rapid horizontal and downward deviation of gaze into the contralateral visual hemifield.     

基于脑微刺激的智能动物的研究

本研究应用自动控制科学和微电子技术，研制开发了适合于自由活动动物的遥控导航系统，并借助于神经生物学和电生理学知识成功的应用于大鼠，使其成为受控于人的“智能动物”。本研究的开展推动了电子信息技术和神经科学的交叉融合，在智能动物的研究方面迈出了成功的一步。     

Gating of tactile input from the hand

Tactile sensations of flutter or pressure were evoked in alert human subjects by intraneural microstimulation in the median nerve. Ratings were obtained of the magnitude of sensations at threshold for conscious detection during movement of the finger to which they were projected, of neighbouring fingers or of the opposite hand. Results showed that inhibition of flutter sensation was maximal in the moved finger (48%), with a weaker graded effect from adjacent (23%) to distant (19%) fingers of the same hand. Sensations of pressure were more markedly suppressed but the gradients were similar. Movement of the opposite hand and isometric contraction of the forearm muscles had little effect. Local anaesthetic blocks of the median and other upper limb nerves counteracted most of the inhibitory effect of movement on cutaneous flutter sensation. We conclude that sensory gating is largely restricted to the moved digits, that it applies to submodalities of both flutter and pressure and that sensory gating is mostly mediated by cutaneous receptor input from the hand.     

Early enhancement but no late changes of motor responses induced by intracortical microstimulation in the ketamine-anesthetized rat

The objectives of this study were to determine whether changes in electromyographic (EMG) responses observed during prolonged intracortical microstimulation (ICMS) were due to local plasticity of the motor system or to global changes in the preparation. Local effects would be expressed as changes only along the activated motor pathway, whereas global effects would be expressed as changes also appearing at distant cortical efferent microzones. The results of ICMS in the ketamine-anesthetized rat showed that the size of consecutive EMG responses increased gradually to a relatively stable magnitude over a period of four to six trains of stimuli. This early enhancement of EMG responses was maintained while continuously providing trains of stimuli at 1 Hz. However, it disappeared after a 5-min period of muscle inactivity. This response enhancement in the presence of ketamine (an NMDA, N-methyl-d-aspartate, receptor blocker) suggests that a neuronal mechanism involving non-NMDA-mediated homosynaptic short-term potentiation (STP) was responsible for the early enhancement of EMG responses. To compare ICMS effects at several time intervals it was necessary to average several evoked EMG responses because there was normal biological variability between single EMG responses. To determine the optimal number of EMG responses that would provide a reliable average EMG response, averages of 5, 10, 15, 20, and 25 EMG responses evoked from a single cortical site were collected at 5-min intervals. The results revealed that averages of 10 responses would provide reliable average EMG responses for all subsequent analyses. There were wide fluctuations in the average EMG responses when periodic injections of ketamine were used to maintain a low reflexive state in the animal. Switching to continuous infusion of ketamine abolished these fluctuations but there remained a small drift in the magnitudes of consecutive EMG responses. To test whether this drift reflected local plastic changes in the motor system induced by stimulation or some global changes, EMG responses evoked from another ICMS site were used as control. The rationale was that global effects would affect all motor output sites equally. The sizes of control EMG responses followed a similar time course to those evoked from the test site. Furthermore, standardizing the test EMG responses with respect to the control responses eliminated the drift in response magnitudes. Thus the drift was due to slow global changes in neuronal excitability possibly produced by the anesthesia. In conclusion, late changes occurring after hours of ICMS were not due to plasticity of the motor system but rather to global changes in the preparation, possibly resulting from the inability to set an ideal anesthetic infusion rate that could maintain a constant level of neuronal excitability over long periods of time. However, there was early enhancement of the EMG responses evoked by ICMS due to neuronal plasticity possibly mediated by a non-NMDA mechanism of homosynaptic STP such as post-tetanic potentiation (PTP). This early enhancement would favor recruitment of the previously activated motor pathway and lead to greater consistency in movement execution.     

Sensorimotor corticocortical projections from rat barrel cortex have an anisotropic organization that facilitates integration of inputs from whiskers in the same row

We used a dual anterograde-tracing paradigm to characterize the organization of corticocortical projections from primary somatosensory (SI) barrel cortex. In one group of rats, biotinylated dextran amine (BDA) and Fluoro-Ruby (FR) were injected into separate barrel columns that occupied the same row of barrel cortex; in the other group, the tracers were deposited into barrel columns residing in different rows. The labeled corticocortical terminals in the primary motor (MI) and secondary somatosensory (SII) cortices were plotted, and digital reconstructions of these plots were quantitatively analyzed. In all cases, labeled projections from focal tracer deposits in SI barrel cortex terminated in elongated, row-like strips of cortex that corresponded to the whisker representations of the MI or SII cortical areas. When both tracers were injected into separate parts of the same SI barrel row, FR- and BDA-labeled terminals tended to merge into a single strip of labeled MI or SII cortex. By comparison, when the tracers were placed in different SI barrel rows, both MI and SII contained at least two row-like FR- and BDA-labeled strips that formed mirror image representations of the SI injection sites. Quantitative analysis of these labeling patterns revealed three major findings. First, labeled overlap in SII was significantly greater for projections from the same barrel row than for projections from different barrel rows. Second, in the infragranular layers of MI but not in the supragranular layers, labeled overlap was significantly higher for projections from the same SI barrel row. Finally, in all layers of SII and in the infragranular layers of MI, the amount of labeled overlap was proportional to the proximity of the tracer injection sites. These results indicate that SI projections to MI and SII have an anisotropic organization that facilitates the integration of sensory information received from neighboring barrels that represent whiskers in the same row.