14 December 2007. Faced with an onslaught of information, the brain has a way of separating the wheat from the chaff. It selects the important and encodes for keeping while ignoring the rest. That ability makes the most of the limited storage capacity of working memory, a readily accessible data cache that we tap into for quick thinking, planning, and other integrated cognitive tasks.
Working memory is stored in the posterior parietal region of the brain, but the location of the gatekeeper for irrelevant information was unknown. New functional MRI data from Fiona McNab and Torkel Klingberg at the Karolinska Institute in Stockholm, Sweden, places that control in the basal ganglia, and more specifically in the globus pallidus. Their work, published in the December 9 issue of Nature Neuroscience, suggests a new role for a brain region more often associated with movement.
In the study, subjects were asked to remember the position of colored dots on a grid. When the test was preceded by a warning to expect irrelevant dots to appear also, the subjects showed anticipatory activation in the prefrontal cortex and basal ganglia. The extent of this activation, particularly in the globus pallidus, correlated with a decreased storage-related signal in the posterior parietal, signifying a selective memory deposition. People with better working memory had more activity in the global pallidus in the face of distracting stimuli, suggesting that their brains might be more efficient at filtering out junk, allowing only the important pieces to take up the limited capacity in the working memory.
The results raise the question of whether damage in the basal ganglia might contribute to dementia. Early in AD, patients develop attentional problems, including an inability to filter out distractions, and to multitask (MacPherson et al., 2007). These problems could reflect a deficit in working memory, which is closely connected to attention. Amyloid deposition is seen fairly broadly distributed across the brain in AD cases that come to autopsy. A recent imaging study on two families with early-onset AD presenilin mutations revealed deposition of amyloid in the striatal region of the basal ganglia in young, asymptomatic members (see ARF related news story). In an e-mail, Klingberg told Alzforum, “It is too early to say anything specific about the implications for AD. This paper is mainly about finding the mechanisms behind filtering, and the link to working memory. But it’s a start. We have not decided in what directions we will proceed, but childhood development as well as clinical applications are both interesting options.” Of interest, the striatal region of the basal ganglia is also compromised in Parkinson disease, which sometimes causes dementia along with motor symptoms.—Pat McCaffrey.
McNab F, Klingberg T. Prefrontal cortex and basal ganglia control access to working memory. Nat Neurosci. 2007 Dec 9 [Epub ahead of print] Abstract