Mechanism for top-down control of working memory capacity

Abstract

Working memory capacity, the maximum number of items that we can transiently store in working memory, is a good predictor of our general cognitive abilities. Neural activity in both dorsolateral prefrontal cortex and posterior parietal cortex has been associated with memory retention during visuospatial working memory tasks. The parietal cortex is thought to store the memories. However, the role of the dorsolateral prefrontal cortex, a top-down control area, during pure information retention is debated, and the mechanisms regulating capacity are unknown. Here, we propose that a major role of the dorsolateral prefrontal cortex in working memory is to boost parietal memory capacity. Furthermore, we formulate the boosting mechanism computationally in a biophysical cortical microcircuit model and derive a simple, explicit mathematical formula relating memory capacity to prefrontal and parietal model parameters. For physiologically realistic parameter values, lateral inhibition in the parietal cortex limits mnemonic capacity to a maximum of 2-7 items. However, at high loads inhibition can be counteracted by excitatory prefrontal input, thus boosting parietal capacity. Predictions from the model were confirmed in an fMRI study. Our results show that although memories are stored in the parietal cortex, interindividual differences in memory capacity are partly determined by the strength of prefrontal top-down control. The model provides a mechanistic framework for understanding topdown control of working memory and specifies two different contributions of prefrontal and parietal cortex to working memory capacity.computer model ͉ fMRI ͉ lateral inhibition ͉ prefrontal ͉ short-term memory ͉ parietal

Re-evaluating the relationships among filtering activity, unnecessary storage, and visual working memory capacity

“…Consequently, it will be critical for future studies to determine how to identify filtering-related activity in the absence of distractors, or how to better operationalize the activity observed during filtering. A potential candidate for such activity may be provided by a study that found a positive correlation between VWM capacity (which was measured both by behavioral performance and by the amount of BOLD signal observed in the IPS) and activity in the DLPFC (Edin et al, 2009). The authors of this study suggested that VWM capacity was partly determined by topdown control driven by activity originating in the DLPFC, even when distractors were not present.…”

Repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex enhances working memory

“…DLPFC has been associated with the encoding and retrieval phases of WM tasks (Balconi 2013), and consistent evidence implicates parietal areas in the actual storage of information (Edin et al 2009). DLPFC may regulate the signal-tonoise ratio of the parietal cortex to enable increased storage capacity (Edin et al 2009).…”

“…DLPFC has been associated with the encoding and retrieval phases of WM tasks (Balconi 2013), and consistent evidence implicates parietal areas in the actual storage of information (Edin et al 2009). DLPFC may regulate the signal-tonoise ratio of the parietal cortex to enable increased storage capacity (Edin et al 2009). Prior electrophysiological studies have shown that high-frequency rTMS can entrain endogenous alpha frequency in the stimulated area, which then leads to suppression of distracters and thus enhancement of WM capacity (Sauseng et al 2009;Hamidi et al 2009;Thut and Miniussi 2009;Klimesch et al 2003).…”

“…Human and animal research has provided key insights into the neuronal and neurotransmitter basis of WM, with the dorsolateral prefrontal cortex (DLPFC) assuming an executive role by exerting top-down control over other WM-related brain areas, including the intraparietal sulcus and posterior parietal cortex (Gazzaley and Nobre 2012;Zanto et al 2011;Edin et al 2009;Kojima and Goldman-Rakic 1982). Brain imaging studies in humans using functional magnetic resonance imaging (fMRI) and positron emission tomography have shown increased activation of the DLPFC in WM tasks (Owen et al 1996;Wager and Smith 2003;Cho & Strafella 2009).…”

A computational model of fMRI activity in the intraparietal sulcus that supports visual working memory

“…Consequently, the working memory capacity of the whole network will increase in the same way as for selfexcitation. A similar idea was put forward by Edin et al (2009), who identified dorsolateral prefrontal cortex as a source of top-down modulatory signals to the parietal cortex.…”