Do motor plans affect sensorimotor state estimates during temporal decision-making with crossed vs. uncrossed hands? Failure to replicate the dynamic crossed-hand effect.

Hermosillo et al. (J Neurosci 31: 10019-10022, 2011) have suggested that action planning of hand movements impacts decisions about the temporal order judgments regarding vibrotactile stimulation of the hands. Specifically, these authors reported that the crossed-hand effect, a confusion about which hand is which when held in a crossed posture, gradually reverses some 320 ms before the arms begin to move from an uncrossed to a crossed posture or vice versa, such that the crossed-hand is reversed at the time of movement onset in anticipation of the movement's end position. However, to date, no other study has attempted to replicate this dynamic crossed-hand effect. Therefore, in the present study, we conducted four experiments to revisit the question whether preparing uncrossed-to-crossed or crossed-to-uncrossed movements affects the temporo-spatial perception of tactile stimulation of the hands. We used a temporal order judgement (TOJ) task at different time stages during action planning to test whether TOJs are more difficult with crossed than uncrossed hands ("static crossed-hand effect") and, crucially, whether planning to cross or uncross the hands shows the opposite pattern of difficulties ("dynamic crossed-hand effect"). As expected, our results confirmed the static crossed-hand effect. However, the dynamic crossed-hand effect could not be replicated. In addition, we observed that participants delayed their movements with late somatosensory stimulation from the TOJ task, even when the stimulations were meaningless, suggesting that the TOJ task resulted in cross-modal distractions. Whereas the current findings are not inconsistent with a contribution of motor signals to posture perception, they cast doubt on observations that motor signals impact state estimates well before movement onset.

Working memory in action: Transsaccadic working memory deficits in the left visual field and after transcallosal remapping.

Every waking second, we make three saccadic eye movements that move our retinal images. Thus, to attain a coherent image of the world we need to remember visuo-spatial information across saccades. But transsaccadic working memory (tWM) remains poorly understood. Crucially, there has been a debate whether there are any differences in tWM for the left vs. right visual field and depending on saccade direction. However, previous studies have probed tWM with minimal loads whereas spatial differences might arise with higher loads. Here we employed a task that probed higher memory load for spatial information in the left and right visual field and with horizontal as well as vertical saccades. We captured several measures of precision and accuracy of performance that, when submitted to principal component analysis, produced two components. Component 1, mainly associated with precision, yielded greater error for the left than the right visual field. Component 2 was associated with performance accuracy and unexpectedly produced a disadvantage after rightward saccades. Both components showed that performance was worse when rightward or leftward saccades afforded a shift of memory representations between visual fields compared to remapping within the same field. Our study offers several novel findings. It is the first to show that tWM involves at least two components likely reflecting working memory capacity and strategic aspects of working memory, respectively. Reduced capacity for the left, rather than the right visual field is consistent with how the left and right visual fields are known to be represented in the two hemispheres. Remapping difficulties between visual fields is consistent with the limited information transfer across the corpus callosum. Finally, the impact of rightward saccades on working memory might be due to greater interference of the accompanying shifts of attention. Our results highlight the dynamic nature of transsaccadic working memory.

Effects of endocannabinoid system modulation on social behaviour: A systematic review of animal studies.

There is a clear link between psychiatric disorders and social behaviour, and evidence suggests the involvement of the endocannabinoid system (ECS). A systematic review of preclinical literature was conducted using MEDLINE (PubMed) and PsychINFO databases to examine whether pharmacological and/or genetic manipulations of the ECS alter social behaviours in wildtype (WT) animals or models of social impairment (SIM). Eighty studies were included. Risk of bias (RoB) was assessed using SYRCLE's RoB tool. While some variability was evident, studies most consistently found that direct cannabinoid receptor (CBR) agonism decreased social behaviours in WT animals, while indirect CBR activation via enzyme inhibition or gene-knockout increased social behaviours. Direct and, more consistently, indirect CBR activation reversed social deficits in SIM. These CBR-mediated effects were often sex- and developmental-phase-dependent and blocked by CBR antagonism. Overall, ECS enzyme inhibition may improve social behaviour in SIM, suggesting the potential usefulness of ECS enzyme inhibition as a therapeutic approach for social deficits. Future research should endeavour to elucidate ECS status in neuropsychiatric disorders characterized by social deficits.