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Notes: Abstract  Temporary inactivation of the cerebellar interposed nuclei was used to assess the role of the intermediate cerebellum in the performance of forelimb cutaneo-muscular reflexes in the cat. The following types of reflexive responses were evaluated: the classically conditioned and unconditioned forelimb withdrawal responses and the forelimb tactile placing, hopping and magnet responses. The experiments tested the hypothesis that the intermediate cerebellum is involved in the performance of all the above forelimb reflexes. The forelimb withdrawal reflex was classically conditioned in a newly developed paradigm in which animals were first operantly conditioned to stand on four elevated platforms. Trained animals were microinjected with a γ-aminobutyric acid (GABA) agonist, muscimol, in the interposed nuclei, and the effects of inactivation of the intermediate cerebellar output on the forelimb reflexes were examined. The main findings of these experiments are that unilateral muscimol inactivation of the interposed nuclei in the cat abolished the expression of the classically conditioned limb flexion reflex, suppressed the performance of the unconditioned withdrawal reflex and, in parallel, downregulated the tactile placing, hopping and magnet postural responses in the ipsilateral forelimb. These observations are inconsistent with concepts indicating exclusive involvement of the intermediate cerebellum in the classically conditioned reflexes elicited by aversive stimuli. On the contrary, they support the hypothesis of a more global involvement of this structure in learned and unlearned defensive flexion reflexes and in automatic postural response systems.

Notes: Summary The responses of mossy fibers (MF), granular cells (GrC) and Purkinje cells (PC) were recorded in the cerebellum of the decerebrate cat during a passive movement about the forepaw wrist joint. Three main discharge patterns containing information about all the static and dynamic parameters of the movement were found. Simultaneous recording of complex spikes (CS) and simple spikes (SS) showed that the activity of PC can be modulated through either MF or CF input channels alone or both together. In the latter case SS and CS discharge most commonly showed an opposite behavior, in which the increase of the frequency of one type of spike was accompanied by a decrease of the frequency of the other type. Both inputs displayed tonic and phasic characteristics and all the qualitative discharge patterns observed. Therefore it was concluded that aside from differences in the discharge frequency, both inputs are able to directly signal peripheral events.

Notes: Summary Discharges of Purkinje cells (PCs) with simple (SS) and complex spikes (CS) in the c1zone of lobule Vc of the anterior lobe of the cerebellar cortex were analyzed in the decerebrate cat during a passive movement of the cat forepaw. The CS of the PC responded differentially and/or proportionally to the position of the extremity, amplitude of the movement, velocity and acceleration. Inphase and outphase responses of the climbing fiber (CF) system to sinusoidal movements could depend on the position of the extremity within the operational range. From these results we deduce that peripheral events can be signalled by the CF system. The possible function of the interaction between the two inputs at the PC level is discussed.

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: Abstract The relationship between changes in posture and the performance of a forelimb movement required for a transition between two stance positions was analysed in cats. The task consisted of an operantly conditioned, forelimb stepping movement from one support platform to another located more anterior. The reward was given only after a specific vertical force was applied to the second platform. This ensured that the cat performed a clear transition from its initial stance posture to another requiring a different weight distribution. The strategy adopted by an animal during the conditioned movement was studied by analysing the distribution of the vertical forces as a function of time. Specific quantitative functions were used to describe the weight distribution in the anterior-posterior, right-left and diagonal directions as the task was performed. The temporal parameters characterising this behaviour were not significantly different between animals, except for reaction times. In contrast, spatial parameters reflected in the distribution of vertical forces generated during the performance of the task were characteristic for each animal. As a consequence, a variety of strategies were employed. Nevertheless some general features were found, including the persistence of a diagonal support pattern during the phasic part of the movement, and an initial movement to the side of the forepaw performing the movement. The findings support the view that each animal exhibits a specific strategy for performing this well-learned task, and that the strategy is consistently employed over consecutive trials of the movement.

Notes: Abstract  Numerous experimental approaches are based on evaluating electromyographically recorded muscle activity. Some experiments require a certain level of pre-innervation in a muscle or muscle group whereas others must avoid this. Measured parameters, such as the time to onset of the muscle response to an electrical stimulus, etc., depend critically on the level of pre-innervation. The pre-innervation level is most commonly estimated from parameters such as the force generated by this muscle or the upright posture of a human subject. These methods, however, are indirect and may yield erroneous results. This paper describes an inexpensive method developed for a wide range of applications in muscle-tonus-based experiments, in which the tonus is precisely controlled. A simple electronic circuit is presented by which the level of muscle pre-innervation is directly recorded, monitored and – depending on the experimental approach – also fed back to the subject. Physiological experiments on the flexion reflex in healthy human subjects document the reliability of our electronic device.

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.