CiteULike: Group: Glimcher_Lab - with tag workingmemory

Dissociation Of working memory from decision making within the human prefrontal cortex.

A Bechara — 2006-03-01T14:48:36-00:00

J Neurosci, Vol. 18, No. 1. (1 January 1998), pp. 428-437.

We tested the hypothesis that cognitive functions related to working memory (assessed with delay tasks) are distinct from those related to decision making (assessed with a gambling task), and that working memory and decision making depend in part on separate anatomical substrates. Normal controls (n = 21), subjects with lesions in the ventromedial (VM) (n = 9) or dorsolateral/high mesial (DL/M) prefrontal cortices (n = 10), performed on (1) modified delay tasks that assess working memory and (2) a gambling task designed to measure decision making. VM subjects with more anterior lesions (n = 4) performed defectively on the gambling but not the delay task. VM subjects with more posterior lesions (n = 5) were impaired on both tasks. Right DL/M subjects were impaired on the delay task but not the gambling task. Left DL/M subjects were not impaired on either task. The findings reveal a cognitive and anatomic double dissociation between deficits in decision making (anterior VM) and working memory (right DL/M). This presents the first direct evidence of such effects in humans using the lesion method and underscores the special importance of the VM prefrontal region in decision making, independent of a direct role in working memory.

Selection and Maintenance of Saccade Goals in the Human Frontal Eye Fields.

Clayton E Curtis — 2006-02-11T09:25:27-00:00

J Neurophysiol (8 February 2006)

In a delayed-response task, response selection marks an important transition from sensory to motor processing. Using event-related fMRI, we imaged the human brain during performance of a novel delayed-saccade task that isolated response selection from visual encoding and motor execution. The frontal eye-fields (FEF) and intraparietal sulcus (IPS) both showed robust contra-lateralized activity time-locked to response selection. Moreover, response selection affected delay-period activity differently in these regions; it persisted throughout the memory delay period following response selection in the FEF, but not IPS. Our results indicate that the FEF and IPS both make important but distinct contributions to spatial working memory. The mechanism that the FEF uses to support spatial working memory is tied to the selection and prospective coding of saccade goals, while the role of the IPS may be more tied to retrospective coding of sensory representations.

Flexible Control of Mutual Inhibition: A Neural Model of Two-Interval Discrimination

Christian Machens — 2005-03-14T21:51:08-00:00

Science, Vol. 307, No. 5712. (18 February 2005), pp. 1121-1124.

Networks adapt to environmental demands by switching between distinct dynamical behaviors. The activity of frontal-lobe neurons during two-interval discrimination tasks is an example of these adaptable dynamics. Subjects first perceive a stimulus, then hold it in working memory, and finally make a decision by comparing it with a second stimulus. We present a simple mutual-inhibition network model that captures all three task phases within a single framework. The model integrates both working memory and decision making because its dynamical properties are easily controlled without changing its connectivity. Mutual inhibition between nonlinear units is a useful design motif for networks that must display multiple behaviors.

Selective representation of relevant information by neurons in the primate prefrontal cortex.

G Rainer — 2005-02-18T15:50:54-00:00

Nature, Vol. 393, No. 6685. (11 June 1998), pp. 577-579.

The severe limitation of the capacity of working memory, the ability to store temporarily and manipulate information, necessitates mechanisms that restrict access to it. Here we report tests to discover whether the activity of neurons in the prefrontal (PF) cortex, the putative neural correlate of working memory, might reflect these mechanisms and preferentially represent behaviourally relevant information. Monkeys performed a 'delayed-matching-to-sample' task with an array of three objects. Only one of the objects in the array was relevant for task performance and the monkeys needed to find that object (the target) and remember its location. For many PF neurons, activity to physically identical arrays varied with the target location; the location of the non-target objects had little or no influence on activity. Information about the target location was present in activity as early as 140ms after array onset. Also, information about which object was the target was reflected in the sustained activity of many PF neurons. These results suggest that the prefrontal cortex is involved in selecting and maintaining behaviourally relevant information.

Temporal structure in neuronal activity during working memory in macaque parietal cortex.

B Pesaran — 2005-02-08T16:23:57-00:00

Nat Neurosci, Vol. 5, No. 8. (August 2002), pp. 805-811.

Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spectral analysis, we found spatially tuned elevated power in the gamma band (25-90 Hz) in LFP and spiking activity during the memory period. Spiking and LFP activity were also coherent in the gamma band but not at lower frequencies. Finally, we decoded LFP activity on a single-trial basis and found that LFP activity in parietal cortex discriminated between preferred and anti-preferred direction with approximately the same accuracy as the spike rate and predicted the time of a planned movement with better accuracy than the spike rate. This finding could accelerate the development of a cortical neural prosthesis.

Phase locking of single neuron activity to theta oscillations during working memory in monkey extrastriate visual cortex.

H Lee — 2005-02-08T14:15:45-00:00

Neuron, Vol. 45, No. 1. (6 January 2005), pp. 147-156.

Working memory has been linked to elevated single neuron discharge in monkeys and to oscillatory changes in the human EEG, but the relation between these effects has remained largely unexplored. We addressed this question by measuring local field potentials and single unit activity simultaneously from multiple electrodes placed in extrastriate visual cortex while monkeys were performing a working memory task. We describe a significant enhancement in theta band energy during the delay period. Theta oscillations had a systematic effect on single neuron activity, with neurons emitting more action potentials near their preferred angle of each theta cycle. Sample-selective delay activity was enhanced if only action potentials emitted near the preferred theta angle were considered. Our results suggest that extrastriate visual cortex is involved in short-term maintenance of information and that theta oscillations provide a mechanism for structuring the recurrent interaction between neurons in different brain regions that underlie working memory.