Mental images across the adult lifespan: a behavioural and fMRI investigation of motor execution and motor imagery.

Motor imagery (M.I.) is a mental state in which real movements are evoked without overt actions. There is some behavioural evidence that M.I. declines with ageing. The neurofunctional correlates of these changes have been investigated only in two studies, but none of the these studies has measured explicit correlations between behavioural variables and the brain response, nor the correlation of M.I. and motor execution (M.E.) of the same acts in ageing. In this paper, we report a behavioural and functional magnetic resonance imaging (fMRI) experiment that aimed to address this issue. Twenty-four young subjects (27 ± 5.6 years) and twenty-four elderly subjects (60 ± 4.6 years) performed two block-design fMRI tasks requiring actual movement (M.E.) or the mental rehearsal (M.I.) of finger movements. Participants also underwent a behavioural mental chronometry test in which the temporal correlations between M.I. and M.E. were measured. We found significant neurofunctional and behavioural differences between the elderly subjects and the young subjects during the M.E. and the M.I. tasks: for the M.E. task, the elderly subjects showed increased activation in frontal and prefrontal (pre-SMA) cortices as if M.E. had become more cognitively demanding; during the M.I. task, the elderly over-recruited occipito-temporo-parietal areas, suggesting that they may also use a visual imagery strategy. We also found between-group behavioural differences in the mental chronometry task: M.I. and M.E. were highly correlated in the young participants but not in the elderly participants. The temporal discrepancy between M.I. and M.E. in the elderly subjects correlated with the brain regions that showed increased activation in the occipital lobe in the fMRI. The same index was correlated with the premotor regions in the younger subjects. These observations show that healthy elderly individuals have decreased or qualitatively different M.I. compared to younger subjects.

dgq: a drosophila gene encoding a visual system-specific G alpha molecule.

We describe the isolation and preliminary characterization of a new G alpha gene (dgq) in Drosophila. The dgq gene is differentially spliced, yielding two putative proteins, both of which contain guanine nucleotide binding and hydrolysis domains and share 50% identity with transducins and other G proteins. These proteins represent a new class of G alpha subunits because they lack both high amino acid identity with other G alpha proteins and the pertussis toxin ADP ribosylation site. The dgq mRNA is detected by RNA-RNA Northern hybridization in wild-type heads but not in wild-type bodies or in the mutant eyes absent heads. Tissue in situ hybridization detects dgq expression only in the retina and ocellus of the adult head, making it a prime candidate for encoding the Drosophila transducin analog, the G protein required for phototransduction.

Nausea and vomiting and dietary cravings and aversions during pregnancy in South African women.

Frequency and severity of nausea and of vomiting during pregnancy, and of pronounced dietary cravings and aversions, were determined in a series of South African rural and urban black, Indian, coloured (European-African-Malay) and white women. Frequency of severe nausea ranged from 3.8% in rural blacks to 19.8% in white women, and of severe vomiting from 3.1% in rural blacks to 17.8% in white and Indian women. Proportions in the other groups were intermediate. Pronounced cravings, claimed by 67-84% in the various groups, included sour, savoury and sweet foods, also fruit and milk. Aversions were claimed by 45-81% of the women in the different groups with meat, fish, coffee and fatty foods, the foods most often avoided. Pica, the consumption of such substances as earth, clay, varied ethnically and regionally; frequency was high in rural and urban black women (44.0% and 38.3%), but much lower (5%) in Indian, coloured and white women.