Working Memory Active short-term memory – Maintenance of task-relevant information online. Keeps relevant information available. Like RAM in a computer Close correspondence between working memory and consciousness

Delayed response tasks are used to WM in animals Spatial delayed response Object delayed response also alternation tasks In all cases, a response is based on some previous event that is relevant on the current trial, but not necessarily the next.

Sample What Delay Test Array Where Delay What-Then-Where Task 4 objects and 4 locations were used Choice

Fixation (2000 msec) Sample (500 msec) Delay (1000 msec) Test (500 msec) S1 S2 S3 C1 C2 C3 Delayed paired associate task

Important features of WM tasks A cue is followed by a delay and then two or more choices Delay is relatively short (about a second to about a minute). Small number of cues that are used repeatedly. A single cue is only relevant for one trial at a time and animals must remember

Delay tasks require that: 1.Animals discriminate among cues 2.Maintain memory across a delay 3.Evaluate choice phase and make correct decision

Brain areas involved in WM?

Today’s take-home message: Working memory is not simply short-term memory. It is an active process in which subjects must select and maintain information. It is under volitional control.

Two fundamental observations of behavior during a typical WM task (delayed match-to-sample) 1. Performance increases with increases in sample Correct choice SampleDelay Test Time 2. Performance decreases with increases in the delay (Much of this work has been conducted in pigeons)

Also: Match rule retained in reference memory. The copy/trace model was meant to highlight what WM is NOT.

Other observations of DMS performance: 1. Changing the illumination of the testing box during retention interval interferes w/ performance. (doesn't matter whether light->dark dark->light) This depends on degree of "surprise". It will habituate. Expected events have no effect on performance. 2. Surprising samples are more memorable. Suggests that animals actively process info about the SM during delay. When surprised, attentional resources drawn to event, less left for actively maintaining the sample. Another example: Directed Forgetting

Next: Neurophysiological evidence for WM as an active process

Sample What Delay Test Array Where Delay What-Then-Where Task 4 objects and 4 locations were used Choice

'What" Delay Activity in PF Cortex: Single Cell Time from sample onset (msec) Spikes per second 'What' Delay'Where' Delay Sample “A” Sample “B” a40_1_01

'What' and 'Where' Delay Activity: Single Cell 'What' Delay Time from sample onset (msec) Spikes per second Sample A Sample B a43_1_32 'Where' Delay Down Up

A monkey test of attention

Sample Array Trials DelayTest stimuli NonmatchMatch Remember the identity and location of only the relevant object Cue Trials 750 msec1500 msec Bar release

Neural correlate of awareness in the prefrontal cortex Time from sample onset (msec) Spikes per second Time from sample onset SampleTest “A” alone“B” alone

Neural correlate of awareness in the prefrontal cortex Time from sample onset (msec) Spikes per second Time from sample onset SampleTest Attend “A”“A” alone“B” alone

Neural correlate of awareness in the prefrontal cortex Time from sample onset (msec) Spikes per second Time from sample onset SampleTest Attend “A”“A” alone Attend “B” “B” alone

WM is not a passive copy of a sensory stimulus instead an active process So, in contrast to the copy/trace model, WM is: 1. Active - Ss actively select, encode and maintain, what is held in WM. 2. Not a simple match rule. Simple maintenance of record of sample then application of a matching rule. Rather something more complex is going on. One thing that may be happening is that instead of a matching rule, Ss develop an expectation, they anticipate what is going to happen and base their behavior on this expectation

What is info is maintained in the delay of WM tasks? Retrospective versus Prospective processing Correct choice SampleDelay Test Time

There is a considerable amount of evidence that animals tend to rely on a prospective code for performance in delay tasks. In symbolic DMS, increasing the delay between sample and choice stimuli causes an increase confusions between similar choice stimuli, not similar samples. Fixation (2000 msec) Sample (500 msec) Delay (1000 msec) Test (500 msec) S1 S2 S3 C1 C2 C3

Fixation (2000 msec) Sample (500 msec) Delay (1000 msec) Test (500 msec) S1 S2 S3 C1 C2 C3 Delayed paired associate task

Conclusions Working memory is an active process. It is under volitional control and can be contrasted with passive or automatic forms of memory. Working memory is prospective. It is geared toward the future, not merely a record of past events.