Rat cerebellar cortex in vitro responds specifically to moving stimuli

Cerebellar Coordination of Neuronal Communication in Cerebral Cortex

Cognitive processes involve precisely coordinated neuronal communications between multiple cerebral cortical structures in a task specific manner. Rich new evidence now implicates the cerebellum in cognitive functions. There is general agreement that cerebellar cognitive function involves interactions between the cerebellum and cerebral cortical association areas. Traditional views assume reciprocal interactions between one cerebellar and one cerebral cortical site, via closed-loop connections. We offer evidence supporting a new perspective that assigns the cerebellum the role of a coordinator of communication. We propose that the cerebellum participates in cognitive function by modulating the coherence of neuronal oscillations to optimize communications between multiple cortical structures in a task specific manner.

Exploring the significance of morphological diversity for cerebellar granule cell excitability

The relatively simple and compact morphology of cerebellar granule cells (CGCs) has led to the view that heterogeneity in CGC shape has negligible impact upon the integration of mossy fibre (MF) information. Following electrophysiological recording, 3D models were constructed from high-resolution imaging data to identify morphological features that could influence the coding of MF input patterns by adult CGCs. Quantification of MF and CGC morphology provided evidence that CGCs could be connected to the multiple rosettes that arise from a single MF input. Predictions from our computational models propose that MF inputs could be more densely encoded within the CGC layer than previous models suggest. Moreover, those MF signals arriving onto the dendrite closest to the axon will generate greater CGC excitation. However, the impact of this morphological variability on MF input selectivity will be attenuated by high levels of CGC inhibition providing further flexibility to the MF → CGC pathway. These features could be particularly important when considering the integration of multimodal MF sensory input by individual CGCs.

From cerebellar texture to movement optimization

The cerebellum is a major site for supervised procedural learning and appears to be crucial for optimizing sensorimotor performance. However, the site and origin of the supervising signal are still elusive. Furthermore, its relationship with the prominent neuronal circuitry remains puzzling. In this paper, I will review the relevant information and seek to synthesize a working hypothesis that explains the unique cerebellar structure. The aim of this review was to link the distinctive functions of the cerebellum, as derived from cerebellar lesion studies, with potential elementary computations, as observed by a bottom-up approach from the cerebellar microcircuitry. The parallel fiber geometry is ideal for performing millisecond computations that extract instructive signals. In this scenario, the higher time derivatives of kinematics such as acceleration and/or jerk that occur during motor performance are detected via a tidal wave mechanism and are used (with appropriate gating) as the instructive signal to guide motor smoothing. The advantage of such a mechanism is that movements are optimized by reducing "jerkiness" which, in turn, lowers their energy requirements.

Consensus paper: pathological role of the cerebellum in autism

There has been significant advancement in various aspects of scientific knowledge concerning the role of cerebellum in the etiopathogenesis of autism. In the current consensus paper, we will observe the diversity of opinions regarding the involvement of this important site in the pathology of autism. Recent emergent findings in literature related to cerebellar involvement in autism are discussed, including: cerebellar pathology, cerebellar imaging and symptom expression in autism, cerebellar genetics, cerebellar immune function, oxidative stress and mitochondrial dysfunction, GABAergic and glutamatergic systems, cholinergic, dopaminergic, serotonergic, and oxytocin-related changes in autism, motor control and cognitive deficits, cerebellar coordination of movements and cognition, gene-environment interactions, therapeutics in autism, and relevant animal models of autism. Points of consensus include presence of abnormal cerebellar anatomy, abnormal neurotransmitter systems, oxidative stress, cerebellar motor and cognitive deficits, and neuroinflammation in subjects with autism. Undefined areas or areas requiring further investigation include lack of treatment options for core symptoms of autism, vermal hypoplasia, and other vermal abnormalities as a consistent feature of autism, mechanisms underlying cerebellar contributions to cognition, and unknown mechanisms underlying neuroinflammation.

Microelectronic system for high-resolution mapping of extracellular electric fields applied to brain slices

There is an enduring quest for technologies that provide - temporally and spatially - highly resolved information on electric neuronal or cardiac activity in functional tissues or cell cultures. Here, we present a planar high-density, low-noise microelectrode system realized in microelectronics technology that features 11,011 microelectrodes (3,150 electrodes per mm(2)), 126 of which can be arbitrarily selected and can, via a reconfigurable routing scheme, be connected to on-chip recording and stimulation circuits. This device enables long-term extracellular electrical-activity recordings at subcellular spatial resolution and microsecond temporal resolution to capture the entire dynamics of the cellular electrical signals. To illustrate the device performance, extracellular potentials of Purkinje cells (PCs) in acute slices of the cerebellum have been analyzed. A detailed and comprehensive picture of the distribution and dynamics of action potentials (APs) in the somatic and dendritic regions of a single cell was obtained from the recordings by applying spike sorting and spike-triggered averaging methods to the collected data. An analysis of the measured local current densities revealed a reproducible sink/source pattern within a single cell during an AP. The experimental data substantiated compartmental models and can be used to extend those models to better understand extracellular single-cell potential patterns and their contributions to the population activity. The presented devices can be conveniently applied to a broad variety of biological preparations, i.e., neural or cardiac tissues, slices, or cell cultures can be grown or placed directly atop of the chips for fundamental mechanistic or pharmacological studies.

On-beam synchrony in the cerebellum as the mechanism for the timing and coordination of movement

In trained reaching rats, we recorded simple spikes of pairs of Purkinje cells that, with respect to each other, were either aligned on a beam of shared parallel fibers or instead were located off beam. Rates of simple spike firing in both on-beam and off-beam Purkinje cell pairs commonly showed great variety in depth of modulation during reaching behavior. But with respect to timing, on-beam Purkinje cell pairs had simple spikes that were tightly time-locked to each other (either delayed or simultaneous) and to movement, despite the variability in rate. By contrast, off-beam Purkinje cell pairs had simple spikes that were not time-locked to each other, neither delayed nor simultaneous. We discuss the implications of these observations for the cerebellar role in timing and coordinating movement.

Detection of sequences in the cerebellar cortex: numerical estimate of the possible number of tidal-wave inducing sequences represented

The two major cortices of the brain--the cerebral and cerebellar cortex--are massively connected through intercalated nuclei (pontine, cerebellar and thalamic nuclei). We suggest that the two cortices co-operate by generating precise temporal patterns in the cerebral cortex that are detected in the cerebellar cortex as temporal patterns assembled spatially in the mossy fibers. We will begin by showing that the tidal-wave mechanism works in the cerebellar cortex as a read-out mechanism for such spatio-temporal patterns due to the synchronous activity they generate in the parallel fiber system which drives the Purkinje cells--the output neurons of the cerebellar cortex--to fire action potentials. We will review the anatomy of the mossy fibers and show that within a "beam", or "row" of cerebellar cortex the mossy fibers in principle could embed a vast number of tidal-wave generating sequences. Based on anatomical data we will argue that the cerebellar mossy fiber-granule cell-Purkinje cell system can potentially detect and--through learning--select from an enormous number of spatio-temporal patterns.

In defense of the cerebellum

The very special intrinsic connectivity of the cerebellar cortex plays but a minor role in present-day theories of cerebellar function, and it is hardly used as a source of inspiration for experiments. It is argued here that a direct translation of structure into physiological relations inescapably leads to some propositions about cerebellar function that could be tested experimentally.

Cerebellar structure and function: making sense of parallel fibers

Many parts of the brain have to cooperate in a finely tuned way in order to generate coordinated motor output. Parameters of these cooperations are adjusted during early childhood development and years of motor learning later in life. The cerebellum plays a special role in the concert of these brain structures. With the unusual geometrical arrangement of its neuronal elements, especially of parallel fibers and Purkinje cells the cerebellum is a selective and sensitive detector of a specific class of spatio-temporal activity patterns in the mossy fiber system: sequences of excitatory input which 'move' along the direction of parallel fibers at about 0.5 m/s, i.e. the speed of spike conductance in parallel fibers. Precise spatio-temporal neuronal activity patterns have been shown to occur in two major sources of afference to the cerebellum, the neocortex and the sensory feedback system. Based on our own experimental work and the above-mentioned findings we suggest that the cerebellum detects specific spatio-temporal activity patterns which trigger learned cerebellar output related to motor control and which contributes to the control of precise timing of muscle contraction.

Distribution of mossy fibre rosettes in the cerebellum of cat and mice: evidence for a parasagittal organization at the single fibre level

Mossy fibres are the main afferent input to the granular layer of the cerebellar cortex. In this study, the spatial distribution of the mossy fibres' presynaptic enlargements - the so-called rosettes - were analysed on the single fibre level. Data obtained from the cerebella of cat and mice were compared to look for species differences, and the cerebella of the adult and young mice were also compared to look for developmental changes. The results show that there is a spatial anisotropy in all mossy fibres studied, with neighbouring rosettes being about three times further away from each other along the parasagittal axis and closer to each other in the mediolateral direction. Furthermore, these results suggest that this anisotropy is established at an early developmental stage. The anisotropic orientation of mossy fibres at the single fibre level supports the hypothesis of a timing mechanism in cerebellar function.

Role of climbing fibers in determining the spatial patterns of activation in the cerebellar cortex to peripheral stimulation: an optical imaging study

The spatial patterns of activation in the rat cerebellar cortex evoked by ipsilateral face stimulation were mapped using optical imaging based on the pH sensitive dye, Neutral Red. The aims of the study were to characterize the optical responses evoked by peripheral stimulation and test the hypothesis that the resultant parasagittal banding is due to climbing fiber activation. In the anesthetized rat Crus I and II of the cerebellar cortex were stained with Neutral Red. Epi-fluorescent changes produced by a train of stimuli (5-10s and 4-20 Hz) to the ipsilateral face were monitored in time using a fast, high resolution charge-coupled device camera. The patterns of activation were quantified using a two-dimensional fast Fourier transform analysis that removed signals with high spatial frequencies and minimized the contribution of horizontal structural elements (i.e. blood vessels). The dominant spatial pattern of activation evoked by face stimulation was that of parasagittal bands. The bands were highly frequency-dependent and were elicited most strongly by stimulus frequencies in the range of 6-8 Hz. There was a large fall-off in the response for frequencies above and below. The optical signal evoked by face stimulation built up over a period of 10s and then gradually decayed. Within a folium the individual parasagittal bands exhibited some frequency and temporal specificity. Stimulation of the contralateral inferior olive also resulted in the activation of parasagittal bands with characteristics similar to the bands evoked by face stimulation, including a preferred stimulus frequency which peaked at 10 Hz. Injection of lidocaine into the contralateral inferior olive blocked the parasagittal bands evoked by ipsilateral face stimulation, while control injections of saline had no effect. The results confirm that a parasagittal banding pattern is a dominant feature of the functional architecture of the cerebellar cortex. The parasagittal banding pattern observed with Neutral Red is due primarily to the activation of climbing fiber afferents. The frequency tuning of the responses, with the preference for peripheral stimuli of 6-8 Hz, is in agreement with previous findings that the inferior olive is inherently rhythmic. These observations support the hypothesis that inferior olivary neurons are dynamically coupled into groups that activate parasagittal bands of Purkinje cells in the cerebellar cortex. The frequency tuning also supports the hypothesis that the climbing fiber system is involved with timing. Activation of this afferent system may require stimuli with appropriate frequency content and stimuli synchronized to the rhythmicity of the inferior olive.

Exploring a critical parameter of timing in the mouse cerebellar microcircuitry: the parallel fiber diameter

Since the conduction velocity of the parallel fibers is a critical parameter for a theory of timing in the cerebellar cortex, we set out to quantify the diameter of these axons on an ultrastructural level. The overall mean of the fiber diameter was 0.18 microm. Our results confirm that the parallel fibers of the upper molecular layer are significantly thinner than those of the lower layers. Nevertheless, the difference of about 0.02 microm determined by this study is surprisingly small. In addition, the distribution of the fiber diameters of the upper layers differed slightly, but significantly from a normal distribution, partly on account of a positive skew and a positive kurtosis excess. In summary, the results show that there are fewer differences between the parallel fibers of different levels of the molecular layer than previously assumed and that these differences do not contradict a theory of timing in the cerebellar cortex.

Sequential stimulation of rat and guinea pig cerebellar granular cells in vitro leads to increasing population activity in parallel fibers

Sequential stimulation of the granular layer of the cerebellar cortex in vitro using 11 linearly aligned stimulating electrodes leads to massive population activity in the parallel fiber system and to spike activity in Purkinje cells (Heck, D., Neurosci. Lett., 157 (1993) 95-98; Heck, D., Naturwissenschaften, 82 (1995) 201-2030). The induced parallel fiber activity, however, might have been a result of direct stimulation of parallel fibers themselves and not of stimulation of granular cells or their ascending axons. We report here that using sequential 'moving' stimuli and varying the distance covered by the 'movement', parallel fiber population spike amplitude increases with distance and saturates for distances longer than 1.0 mm. This effect cannot be explained if parallel fibers are directly stimulated, but requires stimulation of the granular cells or their ascending axons. We conclude that the population spike activity and Purkinje cell responses induced by sequential stimulation of the granular layer of the cerebellar cortex slices in this and earlier experiments consists of orthodromic parallel fiber spikes.

Dendritic voltage and calcium-gated channels amplify the variability of postsynaptic responses in a Purkinje cell model

The dendrites of most neurons express several types of voltage and Ca2+-gated channels. These ionic channels can be activated by subthreshold synaptic input, but the functional role of such activations in vivo is unclear. The interaction between dendritic channels and synaptic background input as it occurs in vivo was studied in a realistic computer model of a cerebellar Purkinje cell. It previously was shown using this model that dendritic Ca2+ channels amplify the somatic response to synchronous excitatory inputs. In this study, it is shown that dendritic ion channels also increased the somatic membrane potential fluctuations generated by the background input. This amplification caused a highly variable somatic excitatory postsynaptic potential (EPSP) in response to a synchronous excitatory input. The variability scaled with the size of the response in the model with excitable dendrite, resulting in an almost constant coefficient of variation, whereas in a passive model the membrane potential fluctuations simply added onto the EPSP. Although the EPSP amplitude in the active dendrite model was quite variable for different patterns of background input, it was insensitive to changes in the timing of the synchronous input by a few milliseconds. This effect was explained by slow changes in dendritic excitability. This excitability was determined by how the background input affected the dendritic membrane potentials in the preceding 10-20 ms, causing changes in activation of voltage and Ca2+-gated channels. The most important model variables determining the excitability at the time of a synchronous input were the Ca2+-activation of K+ channels and the inhibitory synaptic conductance, although many other model variables could be influential for particular background patterns. Experimental evidence for the amplification of postsynaptic variability by active dendrites is discussed. The amplification of the variability of EPSPs has important functional consequences in general and for cerebellar Purkinje cells specifically. Subthreshold, background input has a much larger effect on the responses to coherent input of neurons with active dendrites compared with passive dendrites because it can change the effective threshold for firing. This gives neurons with dendritic calcium channels an increased information processing capacity and provides the Purkinje cell with a gating function.