Ethanol and Vestibular Stimulation Reveal Simple and Complex Aspects of Cerebellar Heterogeneity

Genetically eliminating Purkinje neuron GABAergic neurotransmission increases their response gain to vestibular motion

Purkinje neurons in the caudal cerebellar vermis combine semicircular canal and otolith signals to segregate linear and gravitational acceleration, evidence for how the cerebellum creates internal models of body motion. However, it is not known which cerebellar circuit connections are necessary to perform this computation. We first showed that this computation is evolutionarily conserved and represented across multiple lobules of the rodent vermis. Then we tested whether Purkinje neuron GABAergic output is required for accurately differentiating linear and gravitational movements through a conditional genetic silencing approach. By using extracellular recordings from lobules VI through X in awake mice, we show that silencing Purkinje neuron output significantly alters their baseline simple spike variability. Moreover, the cerebellum of genetically manipulated mice continues to distinguish linear from gravitational acceleration, suggesting that the underlying computations remain intact. However, response gain is significantly increased in the mutant mice over littermate controls. Altogether, these data argue that Purkinje neuron feedback regulates gain control within the cerebellar circuit.

Characterization of cerebellar ataxia in chronic alcoholics using the International Cooperative Ataxia Rating Scale (ICARS)

BACKGROUND

Alcoholism is the most common cause of cerebellar dysfunction, yet estimates of the incidence of alcoholic cerebellar degeneration (ACD) vary greatly, with differences in methodologies contributing to these disparate findings. This study set out to characterize the frequency and pattern of clinical signs of ACD in an alcoholic group using the International Cooperative Ataxia Rating Scale (ICARS).

METHODS

We compared the performance of 49 alcoholics and 29 control participants. The relative contributions of demographic and alcohol consumption variables to ICARS scores in the alcoholic group were also examined.

RESULTS

The alcoholic group demonstrated significantly poorer performance on all of the ICARS subscales as compared with the control group. Within the alcoholic group, performance was more impaired on the speech scale than on all of the other scales, except the lower limb component of the kinetic scale, and less impaired on the oculomotor scale compared with all other scales. Years of heavy drinking and lifetime alcohol consumption correlated with total ICARS scores; however, maximum daily consumption was actually negatively correlated with ICARS scores. Of the alcohol history variables, years of heavy drinking was the best predictor of total ICARS scores, making a 19% unique contribution, followed by the period of abstinence from alcohol, which uniquely contributed 7% of the variance. There were high correlations between age and male gender and the alcohol consumption variables; however, age and gender were still found to uniquely contribute 5 and 7% respectively to the variance in total ICARS scores.

CONCLUSIONS

ACD may affect up to two-thirds of chronic alcoholics. Assessing the number of years an individual has been drinking beyond a certain threshold can give a good indication of the likelihood of ACD. Age, gender, and the source of the clinical sample may significantly contribute to the prevalence of ACD and require further detailed investigation.

Cerebellar zones: history, development, and function

The longitudinal and transverse zonal arrangement of axonal projections to and from the cerebellum, even more than the well-known laminar cytoarchitecture, is the hallmark of cerebellar anatomy. No model of cerebellar function, whether in motor control, cognition, or emotion, will be complete without understanding the development and function of zones. To this end, a special issue of this journal is dedicated to zones, and the purpose of this article is to summarize the research and review articles that are contained within. The special issue begins by considering some of the very first studies in the 1960s and 1970s that led to our modern understanding of this unique and defining anatomical substructure. Then, it considers the molecular analogs of longitudinal zones in the form of stripes in the cerebellar cortex and related sub-areas in the deep cerebellar nuclei, and it includes studies on the genetic underpinnings of stripes and zones. Several articles address the evolution of both embryonic clusters and adult zones across vertebrate species, and others discuss the functional and clinical relevance of zones. While we do not yet fully understand the role of zones with respect to motor behavior in all of its complexities, cerebellar function is clearly modular, and combinatorial models of complex motor movements based on multi-purpose modules are beginning to emerge. This special issue, by refocusing attention on this fundamental organization of the cerebellum, sets the stage for future studies that will more fully reveal the cellular, developmental, behavioral, and clinical relevance of zones.