Working Memory

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

2. Delayed response tasks are used to WM in animals Spatial delayed responseObject delayed responsealso 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.

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

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

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

6. Delay tasks require that: • Animals discriminate among cues • Maintain memory across a delay • Evaluate choice phase and make correctdecision

7. Brain areas involved in WM?

8. Today’s take-home message: Working memory is not simply short-term memory.It is an activeprocess in which subjects must select andmaintain information. It is under volitional control.

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

10. Also:Match rule retained inreference memory. The copy/trace model was meant to highlight what WMis NOT.

12. 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

13. Next: Neurophysiologicalevidence for WM as anactive process

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

15. 'What" Delay Activity in PF Cortex: Single Cell 'What' Delay 'Where' Delay 100 90 80 Sample “A” 70 Spikes per second 60 50 40 Sample “B” 30 20 0 500 1000 1500 2000 2500 Time from sample onset (msec) a40_1_01

16. 'What' and 'Where' Delay Activity: Single Cell 'Where' Delay 'What' Delay 100 Sample A Down 80 Spikes per second 60 40 Up Sample B 20 1400 1600 1800 2000 2200 2400 2600 2800 0 200 400 600 800 1000 1200 1400 Time from sample onset (msec) a43_1_32

17. A monkey test of attention

23. Remember the identity and location of only the relevant object Sample Delay Test stimuli Array Trials Nonmatch Match Cue Trials 750 msec 1500 msec Bar release

24. Neural correlate of awareness in the prefrontal cortex “A” alone “B” alone 100 Spikes per second 50 Sample Test 0 0 1000 2000 0 1000 2000 Time from sample onset ( msec ) Time from sample onset

25. Neural correlate of awareness in the prefrontal cortex Attend “A” “A” alone “B” alone 100 Spikes per second 50 Sample Test 0 0 1000 2000 0 1000 2000 Time from sample onset ( msec ) Time from sample onset

26. Neural correlate of awareness in the prefrontal cortex Attend “A” “A” alone “B” alone Attend “B” 100 Spikes per second 50 Sample Test 0 0 1000 2000 0 1000 2000 Time from sample onset ( msec ) Time from sample onset

27. 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

28. What is info is maintained in the delayof WM tasks? Retrospective versus Prospective processing Time Correct choice Test Sample Delay

29. 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) S1 C1 Delay (1000 msec) Test (500 msec) S2 C2 S3 C3

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

41. Conclusions Working memory is an active process. It is under volitionalcontrol and can be contrasted with passive or automaticforms of memory.Working memory is prospective. It is geared toward the future, notmerely a record of past events.