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PubMed2002

Correlates of human handedness in primary motor cortex: a review and hypothesis.

A review of the research on anatomical and functional asymmetries in human primary motor cortex suggests that the area of hand representation is greater in the dominant than in the non-dominant hemisphere and that there is a greater dispersion of elementary movement representations with more profuse horizontal connections between them. The more profuse interconnections in motor cortex (M1) of the dominant hemisphere might form a neural substrate which favors the formation of experience-dependent excitatory and inhibitory interactions between elementary movement representations. Motor practice might lead to more precise spatiotemporal coordination of the activity of the elementary movement representations in M1 of the dominant than that of the non-dominant hemisphere, thus leading to more dexterous behavior of the dominant than that of the non-dominant hand.

Functional Laterality↗
PubMed1997

The expression pattern of nodal and lefty in the mouse mutant Ft suggests a function in the establishment of handedness.

We have investigated the expression of left/right (L/R) asymmetry markers, nodal and lefty, in the situs inversus mouse mutant Fused toes (Ft). Both genes exhibited bilateral expression in the lateral plate mesoderm (LPM) at developmental stages whereas in wildtype embryos these genes were found to be expressed exclusively in the left LPM. Inspection of tail location and primitive heart tube looping, structures known to be handed in their orientation, documented a random orientation of these structures. Crossing of the Ft mutation into a different genetic background resulted in a strong reduction of this random orientation. Although the major fraction of these individuals still displayed nodal and lefty on both sides of the LPM, expression was almost always found to be weaker in the right LPM. These results suggest that the establishment of asymmetry is independent of nodal or lefty signals. However, handed asymmetry, which means consistent L/R differences, such as the dextral looping of the primitive heart tube or the right-oriented tail, is directed by differences in the L/R expression pattern of these two genes.

Animals↗
PubMed1995

Cerebral hemispheric asymmetry revisited: effects of handedness, gender and schizophrenia measured by radius of gyration in magnetic resonance images.

Abnormal patterns of cerebral hemispheric asymmetry have been inconsistently reported in association with schizophrenia. Radius of gyration (Rg) is a measure of the mean dispersion of points in a radially organized structure about that structure's centre of gravity. We developed computerized methods for estimating Rg of the magnetic resonance image (MRI) boundary between cortex and subcortex, and applied these methods to measurement of cerebral hemispheric asymmetry in 37 schizophrenics (SZs) and 30 controls (CONs). In right-handed CONs, Rg of right brain boundaries was significantly greater than Rg of left brain boundaries; in left-handed CONs, Rg of left brain boundaries was significantly greater than Rg of right brain boundaries. In right-handed males (both SZ and CON) there were significant differences in Rg between hemispheres; whereas in females (both SZ and CON), there were no such differences. Right-handed male SZs (N = 26) were distinguished by reversal of the right-handed male CON pattern of interhemispheric difference in Rg, and by global reduction in Rg of right brain boundaries. These was no evidence for significant abnormality of Rg in right-handed female SZs (N = 7). There findings suggest an important interactive effect of gender and schizophrenia on lateralized cerebral structure.

Adult↗
PubMed2001

Computing handedness: quantized and superposed switch and dynamic memory of helical polysilylene.

Two new conjugating helical polymers comprising a rodlike silicon backbone and enantiopure chiral pendants, poly[(R)-3,7-dimethyloctyl-(S)-3-methylpentylsilylene] (PS-1) and its diastereomeric poly[(S)-3,7-dimethyloctyl-(S)-3-methylpentylsilylene] (PS-2), were prepared. Molecular mechanics calculations of PS-1 and PS-2 model oligomers indicated a double well potential energy curve corresponding to almost enantiomeric helices with dihedral angles of 150-160 degrees (P-motif, global minimum) and 200-210 degrees (M-motif), regardless of their tacticity. Experimentally, it was found that PS-1 in dilute isooctane revealed switchable ambidextrous helicity on application of a thermal energy bias. Although PS-1 featured three distinct switching regions, viz. "region 1, between -80 and -10 degrees C", "region 2, between -10 and +10 degrees C", and "region 3, between +10 degrees C and +80 degrees C", the switching properties were interpreted as the result of superposed P- and M-helicities, undergoing dynamic pseudo-racemization or oscillation. Oscillating helicity in region 2 was roughly estimated to be about 13 cm(-)(1). The superposed helicity in region 2 was critical since it afforded molecular recognition ability with a dynamic memory function that was highly susceptible to solvent molecular topology and volume fraction. This could lead to potential as a molecular information processor to serve as a gauge of chemical properties. On the other hand, PS-2 could not switch its preferential screw-sense in the range of -80 to +80 degrees C. This may be related to greater differences the potential energy curve between P- and M-motifs.

Journal Article↗
PubMed2005

Turn and helical peptide handedness governed exclusively by side-chain chiral centers.

We have examined the preferred 3D structure of homopeptides based on an alpha-amino acid lacking the asymmetry at the alpha-carbon but exhibiting chirality in the side chains (at the two beta-carbons). These joint stereochemical properties are remarkably unusual for an alpha-amino acid. To this end, we carried out an experimental investigation by X-ray diffraction and NMR spectrometry. The results point to a well-defined relationship between screw sense of the turn and helix structures formed and side-chain configurations.

Cyclopropanes↗