To investigate the effects of aging on coordination of plantar flexor muscles during bipedal and unipedal stances, we examined a relationship between the center of pressure sway and electromyographic activity of these muscles, and also the common neural input, using a coherence analysis. Healthy young and elderly adults were asked to perform bipedal and unipedal standing. The electromyograms were recorded unilaterally from the medial and lateral gastrocnemius (MG and LG) and soleus (SL) muscles, and the common input was analyzed for MG-LG, MG-SL, and LG-SL pairs in two frequency bands: a delta band, that is associated with force variability, and a beta band, that could reflect the corticospinal drive. Main results indicated that the MG and SL muscles worked for lateral sway, while the LG muscle worked for medial sway during the unipedal stance. The delta-band coherence for the MG-SL pair and the beta-band coherences for all the pairs were larger during the unipedal than bipedal stance for both groups. The delta-band coherence for the MG-SL pair was larger for the elderly than young adults during the unipedal stance. In addition, the beta-band coherence for the MG-SL pair was larger than the other pairs during the unipedal stance for the elderly. These findings suggest that the oscillatory activity between the MG and SL muscles is strongly involved in the control of unipedal stance, and aging would increase the cortical drive to these muscles to deal with the postural sway that could be affected by forces generated cooperatively by them.

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Shoaling can be considered a simple form of affective behavior displayed by social fish in which a single fish exhibits an tendency to approach others. In the present study, we adopted a dual approach to investigate shoaling behavior in the medaka fish (Oryzias latipes): a behavioral pharmacological approach to assess mirror approaching behavior and an immunohistochemical approach to examine the neurotransmitter distribution in the medaka telencephalon. In order to gain an insight into shoaling activity, we examined the pharmacological effects of the positive allosteric modulator of the gamma-aminobutyric acid (GABA) anti-anxiety drug, diazepam, and chlorpromazine, a predominantly dopaminergic antagonist on mirror approaching behavior and, in particular, mirror approaching time (MAT; a tendency to shoal) and swimming distance (SWD). Diazepam dose-dependently suppressed MAT, but had no effect on SWD. Conversely, chlorpromazine suppressed SWD without having effects on MAT. The present study demonstrates for the first time that an anti-anxiety drug selectively modifies shoaling behavior in fish. Although the mechanism of this modification remains to be fully identified, immunohistochemical analysis suggests that a positive allosteric modulator of GABA acts on two distinct telencephalic regions. Mirror approaching behavior therefore revealed a close relationship with the action of the GABA-nergic system and not the dopaminergic system in the medaka telencephalon.

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