A voxel-by-voxel parametric fMRI study of motor mental rotation: hemispheric specialization and gender differences in neural processing efficiency.

Differences between men and women in brain size, cognitive performance and lateralization of brain activation have been perennial and controversial issues. Here we show that in a motor mental rotation task where women and men performed equally well, the slope of the functional magnetic resonance imaging (fMRI) blood oxygenation level dependent (BOLD) signal per degree of mental rotation was overall 2.4x higher in men than in women. This was attributed to the much more inefficient engagement (i.e. higher slopes) of the right hemisphere by men (mainly the frontal lobe). These findings indicate that women process information much more efficiently than men, which could offset smaller brain size.

Spinocerebellar ataxia in monozygotic twins.

CONTEXT: Although phenotypic heterogeneity in autosomal dominant spinocerebellar ataxia (SCA) has been explained in part by genotypic heterogeneity, clinical observations suggest the influence of additional factors. OBJECTIVES: To demonstrate, quantitate, and localize physiologic abnormalities attributable to nongenetic factors in the development of hereditary SCA. DESIGN: Quantitative assessments of ocular motor function and postural control in 2 sets of identical twins, one with SCA type 2 and the other with episodic ataxia type 2. SETTING: University laboratory. MAIN OUTCOME MEASURES: Saccadic velocity and amplitude, pursuit gain, and dynamic posturography. RESULTS: We found significant differences in saccade velocity, saccade metrics, and postural stability between each monozygotic twin. The differences point to differential involvement between twins of discrete regions in the cerebellum and brainstem. CONCLUSIONS: These results demonstrate the presence of quantitative differences in the severity, rate of progression, and regional central nervous system involvement in monozygotic twins with SCA that must be owing to the existence of nongermline or external factors.

Novel CACNA1A mutation causes febrile episodic ataxia with interictal cerebellar deficits.

Episodic ataxia type 2 (EA2) is a dominantly inherited disorder, characterized by spells of ataxia, dysarthria, vertigo, and migraines, associated with mutations in the neuronal calcium-channel gene CACNA1A. Ataxic spells lasting minutes to hours are provoked by stress, exercise, or alcohol. Some patients exhibit nystagmus between spells and some develop progressive ataxia later in life. At least 21 distinct CACNA1A mutations have been identified in EA2. The clinical and genetic complexities of EA2 have offered few insights into the underlying pathogenic mechanisms for this disorder. We identified a novel EA2 kindred in which members had ataxic spells induced by fevers or high environmental temperature. We identified a novel CACNA1A mutation (nucleotides 1253+1 G-->A) that was present in all subjects with febrile spells or ataxia. Moreover, we found that, regardless of age or interictal clinical status, all affected subjects had objective evidence of abnormal saccades, ocular fixation, and postural stability. These findings suggest that early cerebellar dysfunction in EA2 results from the intrinsically abnormal properties of the CACNA1A channel rather than a degenerative process.