James M. Bower

Cerebellum implicated in sensory acquisition and discrimination rather than motor control.

Recent evidence that the cerebellum is involved in perception and cognition challenges the prevailing view that its primary function is fine motor control. A new alternative hypothesis is that the lateral cerebellum is not activated by the control of movement per se, but is strongly engaged during the acquisition and discrimination of sensory information. Magnetic resonance imaging of the lateral cerebellar output (dentate) nucleus during passive and active sensory tasks confirmed this hypothesis. These findings suggest that the lateral cerebellum may be active during motor, perceptual, and cognitive performances specifically because of the requirement to process sensory data.

Simulation of networks of spiking neurons: A review of tools and strategies

We review different aspects of the simulation of spiking neural networks. We start by reviewing the different types of simulation strategies and algorithms that are currently implemented. We next review the precision of those simulation strategies, in particular in cases where plasticity depends on the exact timing of the spikes. We overview different simulators and simulation environments presently available (restricted to those freely available, open source and documented). For each simulation tool, its advantages and pitfalls are reviewed, with an aim to allow the reader to identify which simulator is appropriate for a given task. Finally, we provide a series of benchmark simulations of different types of networks of spiking neurons, including Hodgkin–Huxley type, integrate-and-fire models, interacting with current-based or conductance-based synapses, using clock-driven or event-driven integration strategies. The same set of models are implemented on the different simulators, and the codes are made available. The ultimate goal of this review is to provide a resource to facilitate identifying the appropriate integration strategy and simulation tool to use for a given modeling problem related to spiking neural networks.

Acetylcholine and memory

Acetylcholine may set the dynamics of cortical networks to those appropriate for learning of new information, while decreased cholinergic modulation may set the appropriate dynamics for recall. In slice preparations of the olfactory cortex, acetylcholine selectively suppresses intrinsic but not afferent fiber synaptic transmission, while decreasing the adaptation of pyramidal cells. In biologically realistic models of this region, the selective suppression of synaptic transmission prevents recall of previously learned memories from interfering with the learning of new memories, while the decrease in adaptation enhances the response to afferent input and the modification of synapses. This theoretical framework may serve to guide future studies linking neuromodulators to cortical memory function.

Multiple Purkinje Cell Recording in Rodent Cerebellar Cortex.

The spatial and temporal organization of climbing fibre activation of Purkinje cells, the so‐called complex spikes, were studied in the rat cerebellar Crus II folium utilizing a multiple microeletrode recording technique. As many as 32 Purkinje cells could be simultaneously recorded by using a custom‐built electronic amplifier system and a special data storage device. Analysis of the auto‐correlation activity of complex spikes in any given group of Purkinje cells indicated that activation occurs with a particular rhythmicity having a base firing of 10 Hz. Cross‐correlation of spontaneous complex spikes demonstrated, in addition to a particular rhythmicity, an extraordinarily high degree of synchronicity within a particular spatial distribution of Purkinje cells. Thus, Purkinje cells organized in rostra‐caudal rows tend to fire within 1 ms of each other for distances as far as 800 μm (the width of a folium) from the ‘master’ neuron. By contrast, Purkinje cells located medial or lateral to the master neuron showed almost no cross‐correlation. Administration of harmaline to the animal increased the degree of auto‐ and cross‐correlation but did not change the spatial order of the distribution of the cross‐correlation. The results indicate that the olivo‐cerebellar system is organized in such a way that climbing fibre afferents may be activated in a close‐to‐synchronous and rhythmic fashion. The spatial distribution of these afferents over the cortex is such as to activate rostro‐caudal bands of Purkinje cells which tend to fire in a close‐to‐synchronous manner.

Consensus paper: roles of the cerebellum in motor control--the diversity of ideas on cerebellar involvement in movement.

Considerable progress has been made in developing models of cerebellar function in sensorimotor control, as well as in identifying key problems that are the focus of current investigation. In this consensus paper, we discuss the literature on the role of the cerebellar circuitry in motor control, bringing together a range of different viewpoints. The following topics are covered: oculomotor control, classical conditioning (evidence in animals and in humans), cerebellar control of motor speech, control of grip forces, control of voluntary limb movements, timing, sensorimotor synchronization, control of corticomotor excitability, control of movement-related sensory data acquisition, cerebro-cerebellar interaction in visuokinesthetic perception of hand movement, functional neuroimaging studies, and magnetoencephalographic mapping of cortico-cerebellar dynamics. While the field has yet to reach a consensus on the precise role played by the cerebellum in movement control, the literature has witnessed the emergence of broad proposals that address cerebellar function at multiple levels of analysis. This paper highlights the diversity of current opinion, providing a framework for debate and discussion on the role of this quintessential vertebrate structure.

Brain maps and parallel computers

It is well known that neural responses in many brain regions are organized in characteristic spatial patterns referred to as brain maps. It is likely that these patterns in some way reflect aspects of the neural computations being performed, but to date there are no general guiding principles for relating the structure of a brain map to the properties of the associated computation. In the field of parallel computing, maps similar to brain maps arise when computations are distributed across the multiple processors of a parallel computer. In this case, the relationship between maps and computations is well understood and general principles for optimally mapping computations onto parallel computers have been developed. In this paper we discuss how these principles may help illuminate the relationship between maps and computations in the nervous system.

Is the cerebellum sensory for motor's sake, or motor for sensory's sake: The view from the whiskers of a rat?

Publisher Summary This chapter describes a new theory of cerebellar function, which posits that the cerebellum is specifically involved in monitoring and adjusting the acquisition of most of the sensory data on which the rest of the nervous system depends. If correct, the cerebellum is not itself responsible for any particular behaviorally related function but instead facilitates the efficiency with which other structures perform their own functions. In this way the cerebellum may, in fact, be useful but not necessary for brain function as a whole. The idea that the cerebellum controls sensory data acquisition has emerged over the past years from the detailed study of a very small region of crus IIA in the lateral hemispheres of the cerebellum of the albino rat. Perhaps the best evidence that the cerebellum is involved in sensory data acquisition control is its involvement in eye movements system. By definition, anything affecting the position of the eyes is directly related to sensory data acquisition, as acquiring visual data is the only thing an animal does with its eyes.

Cerebellum and auditory function: An ALE meta-analysis of functional neuroimaging studies

Over the past two decades neuroimaging data have accumulated showing that the cerebellum, traditionally viewed only as a motor structure, is also active in a wide variety of sensory and cognitive tasks. We have proposed that instead of explicit involvement in any particular motor, sensory, or cognitive task, the cerebellum performs a much more fundamental computation involving the active acquisition of sensory data. We carried out an activation likelihood estimate (ALE) meta‐analysis to determine whether neuroimaging results obtained during a wide range of auditory tasks support this proposal. Specifically, we analyzed the coordinates of 231 activation foci obtained in 15 different auditory studies selected through an extensive search of the positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) literature. The studies selected represent a wide variety of purely auditory tasks using highly controlled synthesized acoustic stimuli. The results clearly revealed that in addition to temporal auditory areas of cerebral cortex, specific regions in the cerebellum are activated consistently across studies regardless of the particular auditory task involved. In particular, one area in left lateral crus I area showed the greatest volume and ALE peak value among the extratemporal regions. A subanalysis was carried out that ruled out the specific association of this cerebellar cluster with attentional demand. The results are consistent with the hypothesis that the cerebellum may play a role in purely sensory auditory processing, and are discussed in light of the broader idea of the cerebellum subserving a fundamental sensory function. Hum Brain Mapp 25:118–128, 2005.

A comparative survey of automated parameter-search methods for compartmental neural models

One of the most difficult and time-consuming aspects of building compartmental models of single neurons is assigning values to free parameters to make models match experimental data. Automated parameter-search methods potentially represent a more rapid and less labor-intensive alternative to choosing parameters manually. Here we compare the performance of four different parameter-search methods on several single-neuron models. The methods compared are conjugate-gradient descent, genetic algorithms, simulated annealing, and stochastic search. Each method has been tested on five different neuronal models ranging from simple models with between 3 and 15 parameters to a realistic pyramidal cell model with 23 parameters. The results demonstrate that genetic algorithms and simulated annealing are generally the most effective methods. Simulated annealing was overwhelmingly the most effective method for simple models with small numbers of parameters, but the genetic algorithm method was equally effective for more complex models with larger numbers of parameters. The discussion considers possible explanations for these results and makes several specific recommendations for the use of parameter searches on neuronal models.

Prolonged responses in rat cerebellar Purkinje cells following activation of the granule cell layer: an intracellular in vitro and in vivo investigation.

We obtained intracellular recordings of 84 Purkinje cells in vitro from guinea pig slices and of 35 cells in vivo from ketamine-anesthetized rats in order to assess detailed properties of synaptic responses in Purkinje cells following granule cell activation. In vitro, electrical stimulation of the granule cell layer underlying recorded Purkinje cells was used in sagittal slices to predominantly activate synapses on ascending granule cell axons. In vivo, stimulation of the upper lip was used to activate Purkinje cells overlying the upper lip patch in the granule cell layer of crus IIa. In the presence of a GABAA antagonist, Purkinje cells at resting membrane potential responded to both electrical stimulation in vitro and peripheral stimulation in vivo, with a depolarization of 1–10 mV amplitude that lasted for 100–300 ms in the absence of climbing fiber input. Similar prolonged depolarizations could also be induced by brief depolarizing current pulses delivered through the recording electrode, demonstrating that either synaptic or direct depolarization may activate inward currents leading to a sustained response. In support of this hypothesis we found that prolonged depolarizations were shortened significantly when stimulation in the granule cell layer or intracellular current pulses were delivered during hyperpolarizing current steps. Stimulation in the granule cell layer or intracellular current pulses delivered during periods of spontaneous somatic spiking resulted in prolonged depolarizations in dendritic recordings, which were accompanied by an increase in somatic spiking frequency. Following upper lip stimulation in vivo, this increase in somatic spiking was interrupted by an inhibition of 10–50 ms duration. In a majority of recordings, this inhibition did not completely abolish prolonged depolarizations, however, and a delayed increase in somatic spike frequency was still observed. These results suggest that prolonged increases in Purkinje cell spike frequency following peripheral stimulation are due to an underlying prolonged dendritic depolarization induced by granule cell input. Further, a single, short burst of input via ascending granule cell axons appears to be sufficient to induce these responses.