Otherwise, the gate is closed and irrelevant information is kept from needlessly occupying MK-2206 capacity. Several computational models of working memory have achieved this gating dynamic using cortico-striatal mechanisms analogous to those described for the motor system. Just

as a cortically represented motor action could cause Go cells to fire via corticostriatal projections, thereby facilitating thalamic-motoneuron information flow for movement programming (as described above), a cortically represented stimulus could also cause Go cells to fire, again via corticostriatal projections, and thereby facilitate thalamic-prefrontal information flow for working memory updating. By contrast, distracting sensory NVP-BGJ398 concentration representations would trigger NoGo cells and so would have negligible thalamoprefrontal influence. By this scheme, updating is favored (and stable maintenance prevented) by input to Go cells, whereas updating is prevented (and stable maintenance favored) by input to

NoGo cells. Thus, the Go/NoGo system is a potent means of circumventing stability/flexibility tradeoffs that plague single-component systems. Several features of this and related striatal input gating models are supported by human neuroscience evidence. First, there is evidence that D1-expressing Go cells support the rapid updating of information in working memory. Striatal activation in fMRI, thought to be driven primarily by D1 receptor activation [24] is a common observation during working memory tasks that require updating

(Figure 2a). Training of updating transfers to other tasks involving overlapping striatal BOLD responses [25]; this transfer is accompanied by alterations in the striatal hemodynamic response to updating challenges [26] and results in increased striatal dopamine receptor binding [27] (Figure 2b) as assessed via PET. Shifting the striatal balance toward Go firing (via blockade of D2 receptors with P-type ATPase haloperidol) also enhances working memory updating [28]. Second, there is evidence that D2-expressing NoGo cells act to limit the rapid updating of information in working memory. For example, the ‘attentional blink’ is more pronounced among individuals with enhanced D2/D3 receptor binding in the BG [29•] (Figure 2c). Likewise, the depletion of central dopamine due to Parkinson’s disease counterintuitively enhances resistance to distraction in these patients, while producing deficits in the updating of working memory [30]. In summary, a variety of recent evidence strongly implicates BG-mediated input gating in working memory updating. It is important to note that BG-mediated gating is unlikely to be the only mechanism by which working memory is updated. For example, dopaminergic projections might directly ‘toggle’ prefrontal ensembles from a labile state to a more stable one, and hence act as a second kind of gating mechanism [21].