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Notes: Summary 1) The present experiments were undertaken to study how information about the parameters of a passive movement is processed at different neuronal levels of the cat cerebellar cortex. The analysis has been performed by recording extracellularly in the intermediate part of the cerebellar anterior lobe from presumed mossy fibres, presumed granule cells, and Purkinje cells with simple spikes and complex spikes. 2) The discharge patterns obtained during passive movements of the cat's forepaw were characterized by components which could be related to dynamic or static parameters of the movement. With respect to the occurrence of dynamic responses, patterns were classified according to a statistically derived measure in three different types. By using the same statistical measure, discharge patterns were additionally classified into two subgroups according to their response components reflecting static parameters. Within the patterns a clearcut relationship between dynamic and static components was observed. The corresponding distributions are shown and discussed. 3) A very interesting result of the classification of cerebellar discharge patterns is that the distribution of the different types depended on the level of integration within the cerebellar cortex. Patterns of the low scale integrated cerebellar input (mossy fibre-system), as well as those of granule cells (the first cerebellar computational niveau), reflected both static and dynamic movement parameters. At the Purkinje cell level (a level with a high degree of convergence) the discharge patterns are characterized predominantly by dynamic responses. 4) The interrelationship between complex- and simple spikes of Purkinje cells was tested by different methods: a) By analyzing the paired values of the mean complex-(CS) and simple spike (SS) discharge probabilities of 110 Purkinje cells a scatter was obtained, indicating an underlying hyperbolic relation (prob(CS) = a/(prob(SS))b). Thus, a high CS discharge probability is accompanied by a low SS probability and vice versa, b) The timelocked complex- and simple spike responses were studied by comparing the similarity of their responses. All combinations of complex- and simple spike patterns were observed, ranging from a sign correct similarity to a mirror image similarity. The distribution of the measure for similarity shows that the mirror image predominated, c) The individual simple spike discharge probability is characterized by a pause evoked by the occurrence of a complex spike event. The simple spike discharge probabilities during an interval preceeding and following a complex spike event were compared. A post climbing pause coefficient was defined as a measure for the effectiveness of the complex spike event. No relationship between these coefficients and the above mentioned measure for similarity was found. Hence, for the Purkinje cell discharging with the simple spikes independent spike generating processes have to be assumed. 5) From these results it can be derived that cerebellar discharge patterns can be classified with respect to responses to static and dynamic parameters of passive limb movements. Based on this classification it appears that the distribution of responses to static and dynamic parameters depends on the computational level within the cerebellar cortex. If both static and dynamic parameters are conveyed by a single unit, a clear relationship between the response components could be observed. However, this effect was independently found at all cerebellar cortical computational levels indicating a functional principle of processing a pair of movement parameters. The interrelation of complex- and simple spike responses to passive movement was further studied. Since transients of complex- and simple spike patterns were observed ranging from two almost identical patterns to mirror image like patterns, it is assumed that under physiological conditions one of the tasks of the climbing fibre system consists of tuning the simple spike discharge according to the peripheral requirements.

Notes: Summary 1) Experiments were designed to detect how static parameters of natural, passive hand movements are encoded and integrated within the cerebellar cortex. For this purpose unit activity was recorded extracellularly from presumed mossy fibres (MF), presumed granule cells (GrC) and from Purkinje cells (PC) discharging with simple spikes (SS) and complex spikes (CS). With respect to the PC, our interest was focussed primarily on the SS activity. The recordings were performed in the intermediate part of the cerebellar anterior lobe of decerebrate cats. The animal's forepaw was passively moved around the wrist joint by an electronically controlled device. The movements were exactly reproducible so that peristimulus time histograms of the unit activity could be constructed. 2) At the input level (MF) and at the first level of integration within the cerebellar cortex (GrC), patterns with similar discharge characteristics were found. Such patterns could, to a limited extent, also be detected at the cerebellar output (SS of PC). However, in most cases of SS discharge, patterns were found with weak correlation between the tonic activity and static parameters of the movements. 3) Absolute paw position, amplitude, and duration of movements were found to be related over wide ranges to the activities of MF and GrC. Absolute position is directly encoded by tonic discharge during the low or high holding phases. Beside this, units were found without a correlation between the tonic discharge and the position of the nonmoving paw. However, in these units it was sometimes observed that the information about the momentary position or the information about the mean position was sometimes conveyed exclusively during the proceeding upward or downward movement. Thus, information about static parameters was transmitted only at times when a dynamic parameter (such as velocity) occurred. This type of position information encoding is termed “indirect mode of transmission”. 4) A specific relationship between SS unit activity of PC and the absolute position of the forepaw or amplitude of the movement could be found primarily by using multiple ramps instead of single ramp movements. This was observed even if both types of ramp movements had the same velocity, individual amplitude, and tested range. However, on multiple ramp movements the paw generally remained for a shorter period at a specific position level as compared to the single ramp movements. 5) Apart from this timing phenomenon, a late movement response was observed, which results in a specific type of position information encoding on multiple ramp functions. 6) These results indicate that static parameters of a passive limb movement are conveyed via the MF input to the cerebellar cortex. Patterns related to these parameters undergo a change within the MF-, GrC-, Parallel fibre-, PC-system. Different modes of encoding these parameters were observed depending primarily on the neuronal niveau within the cerebellar cortex. Tonic discharge related e.g. to limb position was found at MF and GrC level. Such patterns resemble, at least to a certain extent, those obtained from different peripheral receptors. The high tonic SS activity never showed such a strong relationship to static parameters as observed at the input level; static parameters could be resolved only within relatively short periods of time, especially during the dynamic phases of the movement or during short periods immediately following these phases. This implies that the function of this part of the cerebellum, which is to provide correction signals, should be considered as a more dynamic process characterized by evaluating predominantly information about the momentary ongoing movement.

Notes: Summary 1. Nerve impulses from the afferent fibre of the ampullary electroreceptor inIctalurus were recorded and changes of the response characteristics induced by calcium ions in the medium surrounding the fish were examined. 2. Under normal calcium concentration (2 mM/1) set and break of long lasting electrical stimuli lead to frequency changes, which are equal in size (and have opposite direction) for anodal and cathodal currents, respectively. With calcium deficiency only anodal currents evoke a response (Fig. 1). 3. Also in the case of low calcium, responses to intensity steps depend on direct current flow, but are largely unaffected by the d.c.-level under normal and high calcium (Fig. 3). 4. The decline of the frequency response does not alter the height of a succeeding response, and the off-response is fullsized already at the beginning of frequency decline. The response to the second current-step is only influenced by a preceding current onset, if the interval is shorter than 50–90 ms. For longer delays the frequency response is the same as a reaction unaffected by a prestimulus (Figs. 4–6). This time dependent decrease of the prestimulus effect is not seen with low calcium: there is a permanent (sensitivity enhancing) effect of direct current flow (Fig. 7). 5. From these results it has become evident that the differentiating operation mode of the ampullary electroreceptor is based on two different processes: (1) a calcium dependent mechanism, which makes the receptor independent of direct current and (2) the decline of the frequency response during continuous current flow which is not affected by calcium ions.

Notes: Summary Responses to torque step perturbation of the wrist were compared in premotor area (PMA) and motor cortex (MI) neurons of the monkey. A substantial portion (39%) of cells recorded from the PMA had phasic responses with onset latencies as short as those found in MI (mostly between 15 and 50 ms). Responsiveness to small perturbations, directional specificity and linear correlation of phasic responses with the velocity of displacement are properties that were essentially present in the PMA. A role of somatosensory feedback to the PMA in accurate and fast up-dating of movement is suggested. Tonically sustained responses to torque change (mean latency around 60 ms) were encountered in both areas and preferentially in neurons that had a monotonic load-relationship under steady-state condition. Such cortical responses did not exhibit reflex-like features, i.e. no correlation with amplitude of torque step and resulting displacement. Instead, the new load condition seemed to be represented by the tonic response of any particular neuron in accordance with its individual firing rate-load characteristics. These tonic cortical responses may be involved in the swift and effective adaption to the actual load.

Notes: Abstract From three intact and awake monkeys, 149 Purkinje cells and 44 presumed mossy fibres were recorded in the intermediate part of the cerebellar anterior lobe, and this activity was analyzed with regard to different parameters of a passive hand movement. The tonic discharge rate of the simple spikes (SS) varied according to different joint positions only in a single Purkinje cell, whereas such a position relation was found in nine out of 44 presumed mossy fibres. A phasic increase of the complex spike (CS) discharge rate of Purkinje cells in response to passive wrist movements usually occurred within 100 ms after movement onset. However, in some units a phase of increased CS rate was observed which lasted for the whole movement duration. The amount of this phasic increase in the CS rate depended on the acceleration of movement, but the SS response to movements of different velocity remained unchanged.

Notes: Summary Single cell activity was studied in the postarcuate premotor area (PMA) and primary motor cortex (MI) of two monkeys performing a load-bearing task with the contralateral hand. Steady-state discharge rates were examined in relation to positional maintenance of the wrist which was held in one of three given positions against graded torques directed towards flexion or extension. Significant and monotonic relationships between tonic firing rate and static torque were found in 41% of 477 MI cells and in only 26% of 470 units studied in PMA. However, for specific cell groups in the PMA the proportion of load-related neurons reached that of the MI samples; this was true for pyramidal tract neurons (PTNs) and for ‘non-PTNs’ if recorded in their vicinity. The most interesting difference pertains to the range of load over which cells in both areas modulated activity. MI neurons showed steepest change of firing rates over a limited range of small torques around zero external load; the population average displayed a sigmoidal relationship. Proportionally more PMA neurons increased their activity over the entire range of torques examined or showed the highest increase with stronger torques; the population average best fitted a quadratic function. The mean firing ratetorque slope of the PMA population was significantly smaller than that of MI. Many cells in either area were related to both torque and joint position and displayed correlates of length-tension properties of muscle. Change of position sensitivity with torque was found to parallel the rate-torque characteristics in individual neurons. Mean position sensitivity of PMA neurons increased with increasing torques in the ‘preferred’ direction. In contrast, greatest position sensitivity of the MI population occurred over the range of low torques, which means a clear quantitative dissociation from the muscular activities. The results suggest differential roles of MI and PMA in the control of ‘fine’ versus ‘gross’ muscular forces. Undoubtedly, some PMA cell elements (possibly certain output neurons) are involved in aspects of postural control of EMG adjustment to load and joint position.