Correlation between individual differences in striatal dopamine and in visual consciousness.

A widely held view on consciousness is that it is related to the 'broadcasting' of sensory information to the whole brain [1-3]. Despite the fact that there is general support for this view, it remains unclear how exactly this broadcasting is established. It has been proposed [2,3] that thalamocortical circuits are an important mediator of such broadcasting, but empirical support for this claim is lacking. In the present study, we investigated this hypothesis by exploiting the well-established, but in this context neglected, fact that thalamocortical connectivity is modulated by dopaminergic activity in the striatum [4]. We used positron emission tomography (PET) to measure individual differences in striatal dopamine (DA) level and we correlated this with individual differences in visual consciousness. Our results show that visual awareness is related to the concentration of endogenous DA or DA receptors in striatal areas, supporting the importance of dopaminergic signalling in visual consciousness.

The commonality of neural networks for verbal and visual short-term memory.

Although many neuroimaging studies have considered verbal and visual short-term memory (STM) as relying on neurally segregated short-term buffer systems, the present study explored the existence of shared neural correlates supporting verbal and visual STM. We hypothesized that networks involved in attentional and executive processes, as well as networks involved in serial order processing, underlie STM for both verbal and visual list information, with neural specificity restricted to sensory areas involved in processing the specific items to be retained. Participants were presented sequences of nonwords or unfamiliar faces, and were instructed to maintain and recognize order or item information. For encoding and retrieval phases, null conjunction analysis revealed an identical fronto-parieto-cerebellar network comprising the left intraparietal sulcus, bilateral dorsolateral prefrontal cortex, and the bilateral cerebellum, irrespective of information type and modality. A network centered around the right intraparietal sulcus supported STM for order information, in both verbal and visual modalities. Modality-specific effects were observed in left superior temporal and mid-fusiform areas associated with phonological and orthographic processing during the verbal STM tasks, and in right hippocampal and fusiform face processing areas during the visual STM tasks, wherein these modality effects were most pronounced when storing item information. The present results suggest that STM emerges from the deployment of modality-independent attentional and serial ordering processes toward sensory networks underlying the processing and storage of modality-specific item information.

Is developmental coordination disorder a motor imagery deficit?

This study investigated the notion that children with developmental coordination disorder (DCD) show a reduced capacity of internally simulating movements of their own body or motor imagery. Using a mental rotation paradigm the contribution of hand posture to laterality/mirror judgments of bodily and alphanumeric stimuli was studied in 13 children with DCD and 13 matched typically developing (TD) children. Children were asked to judge whether the stimulus on display, rotated over -90 degrees , -30 degrees , +30 degrees , or +90 degrees , was a right or left hand or a canonical or mirror-reversed letter. Analysis of accuracy (ACC) and response times (RTs) demonstrated that children with DCD were generally slower and made more errors. RTs to letter stimuli were faster than those to hand stimuli in both DCD and TD children. For both groups RTs profiles were influenced by the orientation of the stimulus, showing longer response times for larger rotations. Clockwise rotations of right hands resulted in slower judgments than did counterclockwise rotations, whereas the reverse was true for left hands. Moreover, the results also indicate a contribution of hand posture to the laterality judgments of hands, with longer RTs when the posture of the participants' hands was opposite to the posture of the hands on display. Importantly, these effects that suggest an imagery strategy engaging motor processes were present in both groups. Apparently, the children with DCD of the present study did rely on motor imagery to solve the mental rotation task; however, their judgments seem to be compromised by a less well-defined internal model.