Cerebellum

The cerebellum is crucial for planning, executing, terminating, and learning movements. The cerebellum compares actual with intended motor performance and optimizes the timing of motor function. Thus, it is important in the adaptation of movement and posture. In addition, the cerebellum contributes to cognition and behavior. The primary fissure divides the cerebellum anatomically into anterior and posterior lobes. The posterior lobe is divided from the flocculonodular lobe by the posterolateral fissure. The cerebellum may also be divided into functional zones, including the vermis (midline), paravermal region, and hemispheres (most lateral).

Palestinians Sidelined in Saudi-Emirati Rapprochement with Israel

This essay examines how and why Saudi Arabia and the United Arab Emirates (UAE) have pursued policies that have aligned closer to Israel since 2011. The disruptive impact of the Arab Spring and its turbulent aftermath altered threat perceptions in Riyadh and Abu Dhabi, which increasingly saw Islamism and Iran as the major sources of regional instability. For Saudi and Emirati leaders committed to adopting a more forceful approach to shaping the post-Arab Spring landscape, Israel no longer represented the primary fissure in Middle Eastern politics. Although the process of creating informal ties between the Gulf states and Israel has been decades in the making, the nature of the post-2011 connections between Saudi Arabia and the UAE with Israel have greater strategic depth and are taking place in a far more open setting than ever before.

Cellular and Axonal Diversity in Molecular Layer Heterotopia of the Rat Cerebellar Vermis

Molecular layer heterotopia of the cerebellar primary fissure are a characteristic of many rat strains and are hypothesized to result from defect of granule cells exiting the external granule cell layer during cerebellar development. However, the cellular and axonal constituents of these malformations remain poorly understood. In the present report, we use histochemistry and immunocytochemistry to identify neuronal, glial, and axonal classes in molecular layer heterotopia. In particular, we identify parvalbumin-expressing molecular layer interneurons in heterotopia as well as three glial cell types including Bergmann glia, Olig2-expressing oligodendrocytes, and Iba1-expressing microglia. In addition, we document the presence of myelinated, serotonergic, catecholaminergic, and cholinergic axons in heterotopia indicating possible spinal and brainstem afferent projections to heterotopic cells. These findings are relevant toward understanding the mechanisms of normal and abnormal cerebellar development.

Cerebellar Cortex Contributions to the Expression and Timing of Conditioned Eyelid Responses

We used micro-infusions during eyelid conditioning in rabbits to investigate the relative contributions of cerebellar cortex and the underlying deep nuclei (DCN) to the expression of cerebellar learning. These tests were conducted using two forms of cerebellum-dependent eyelid conditioning for which the relative roles of cerebellar cortex and DCN are controversial: delay conditioning, which is largely unaffected by forebrain lesions, and trace conditioning, which involves interactions between forebrain and cerebellum. For rabbits trained with delay conditioning, silencing cerebellar cortex by micro-infusions of the local anesthetic lidocaine unmasked stereotyped short-latency responses. This was also the case after extinction as observed previously with reversible blockade of cerebellar cortex output. Conversely, increasing cerebellar cortex activity by micro-infusions of the GABAA antagonist picrotoxin reversibly abolished conditioned responses. Effective cannula placements were clustered around the primary fissure and deeper in lobules hemispheric lobule IV (HIV) and hemispheric lobule V (HV) of anterior lobe. In well-trained trace conditioned rabbits, silencing this same area of cerebellar cortex or reversibly blocking cerebellar cortex output also unmasked short-latency responses. Because Purkinje cells are the sole output of cerebellar cortex, these results provide evidence that the expression of well-timed conditioned responses requires a well-timed decrease in the activity of Purkinje cells in anterior lobe. The parallels between results from delay and trace conditioning suggest similar contributions of plasticity in cerebellar cortex and DCN in both instances.