Handedness for bimanual coordinated actions in infants as a function of grip morphology.

We investigated the emergence of bimanual handedness in tasks involving complementary roles for the two hands, one hand holding a base object and the other hand removing several pieces from the base object. Infants aged 12, 16, and 20 months were tested on bimanual tasks differing mainly in the precision of the movement required to remove the pieces. The results show that the right hand was more often used than the left hand not only to grasp the base object but also to remove the pieces, often after transferring the base object from the right to the left hand. As of 12 months of age, right hand preference for the active part of the bimanual task was stronger in the precision grip than in the whole-hand grip tasks. These results indicate that even though infants often do not anticipate that they will need their preferred hand to remove the pieces, they show clear handedness in such coordinated repeated bimanual actions, and do so to a greater degree on tasks requiring precision grip than on ones requiring whole-hand grip. These results agree with the notion that handedness develops very early and is related to the precision required from the active hand.

Temporal analysis of free exploration of an elevated plus-maze in mice.

The elevated plus-maze (EPM) is a very common rodent test of anxiety. It is based on an approach-avoidance conflict between secure closed arms and aversive open arms. However, discrepancies remain on the interpretation of animals' behavior in this assay. The purpose of our study was to get a better understanding of the mouse behavior in the EPM. We applied a minute-by-minute analysis to compare the behavior of mice forcibly exposed to the maze or set free to explore the maze from a familiar box. Three strains of mice (CD1, BALB/c, and C57Bl/6) were tested. The combination of our different conditions of the test with the minute-by-minute analysis showed that mice did not avoid open arms during the first 2 min of the test when they were forcibly exposed to the EPM. Conversely, free exploration of the EPM resulted in a pattern of behavior characterized by open arm avoidance from the outset, demonstrating that open arm avoidance in mice is unconditioned. These findings generalize across the 3 mouse strains. These data suggest that rodents enter the open arms to complete spatial information about the apparatus as a whole before their natural tendency to avoid them is expressed. Our data also indicate that a detailed behavioral analysis is needed whenever BALB/c mice are to be exposed by force to the EPM. Further studies are required to fully understand the behavior of rodents in the EPM and to avoid false interpretations in the fields of psychopharmacology and behavioral neuroscience.