Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by abnormal expansion of glutamine (Q) encoding CAG repeats in the gene Ataxin-1 (ATXN1). Although motor and balance deficits are the core symptoms of SCA1, cognitive decline is also commonly observed in patients. While mutant ATXN1 is expressed throughout the brain, pathological findings reveal severe atrophy of cerebellar cortex in SCA1 patients. The cerebellum has recently been implicated in diverse cognitive functions, yet to what extent cerebellar neurodegeneration contributes to cognitive alterations in SCA1 remains poorly understood. Much of our understanding of the mechanisms underlying pathogenesis of motor symptoms in SCA1 comes from mouse models. Reasoning that mouse models could similarly offer important insights into the mechanisms of cognitive alterations in SCA1 we tested cognition in several mouse lines using Barnes maze and fear conditioning. We confirmed cognitive deficits in Atxn1154Q/2Q knock-in mice with brain wide expression of mutant ATXN1 and in ATXN1 null mice. We found that shorter polyQ length and haploinsufficiency of ATXN1 do not cause significant cognitive deficits. Finally, ATXN1[82Q] transgenic mice—with cerebellum limited expression of mutant ATXN1—demonstrated milder impairment in most aspects of cognition compared to Atxn1154Q/2Q mice, supporting the concept that cognitive deficits in SCA1 arise from a combination of cerebellar and extra-cerebellar dysfunctions.
The hippocampus is believed to encode episodic memory by binding information about the content of experience within a spatial framework encoding the location of that experience. Previous work implies a distinction between positional inputs to the hippocampus that provide information about an animal′s location and nonpositional inputs which provide information about the content of experience, both sensory and navigational. Here we leverage the phenomenon of "place field repetition" to better understand the functional dissociation between positional and nonpositional inputs to CA1 as rats navigated freely on a novel city-block maze, which combined elements of open-field foraging and linear-track tasks. Unlike typical results in open-field foraging, place fields were directionally tuned on the maze, even though the animal's behavior was not constrained to 1-D trajectories. Repeating fields from the same cell tended to have the same directional preference when the fields were aligned along a linear corridor of the maze, but they showed uncorrelated directional preferences when they were unaligned across different corridors. Lastly, individual fields displayed complex time dynamics which resulted in the population activity changing gradually over the course of minutes. These temporal dynamics were evident across repeating fields of the same cell. These results demonstrate that the positional inputs that drive a cell to fire in similar locations across the maze can be behaviorally and temporally dissociated from the nonpositional inputs that alter the firing rates of the cell within its place fields, thereby increasing the flexibility of the system to encode episodic variables within a stable, spatial framework provided by place cells.
Objective The cerebellum has been identified as the key brain region that modulates reward processing in animal models. Consistently, we recently found that people with cerebellar ataxia have impulsive and compulsive behaviors (ICBs), the main symptoms related to abnormal reward processing. Due to the lack of a validated scale to quantitatively measure ICBs in cerebellar disorders, we aim to develop and validate a new scale, Cerebellar Impulsivity–Compulsivity Assessment (CIA). Methods We recruited 62 cerebellar ataxia cases, categorized into those with ICBs and those without. We developed a preliminary version of CIA, containing 17 questions. We studied the internal consistency, test–retest reliability, and inter‐rater reliability to formulate the final version of CIA, which constitutes only 10 questions. The receiver operating characteristic curve (ROC) was generated to assess the sensitivity and specificity of CIA. Results Cerebellar ataxia cases with ICBs have threefold higher total preliminary CIA scores than those without ICBs (12.06 ± 5.96 vs. 4.68 ± 3.50, p = 0.038 ). Cronbach's alpha revealed good internal consistency across all items ( α > 0.70 ). By performing the test–retest reliability and inter‐rater reliability on the preliminary version of CIA, we excluded seven questions ( r < 0.70) and generated the final version of CIA. Based on the ROC, a score of 8.0 in CIA was chosen as the cut‐off for ICBs in individuals with cerebellar ataxia with 81% sensitivity and 81% specificity. Interpretation CIA is a novel tool to assess ICBs in cerebellar ataxia and broaden our understanding of the cerebellum‐related cognitive and behavioral symptoms.
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