23 Apr 2014

Rainer et al. (1999) ‘Prospective Coding for Objects in Primate Prefrontal Cortex’, notes

Corry Shores
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Gregor Rainer; S. Chenchal Rao; and Earl K. Miller

Prospective Coding for Objects in Primate Prefrontal Cortex

Brief Summary:

This experiment suggests that when we retain visual information, it could be about the prior image we saw and/or about the forthcoming image we anticipate as associating with the prior one.


In the introduction, the authors distinguish remembering and anticipating.

When a delay is imposed between two behaviorally related events, animals can bridge this gap by remembering the event before the delay or anticipating the event after the delay.

They have us consider if the animal is shown two things [lets say red and blue dots] then later must choose one or another thing [for example, if see red, then delay, then must choose circle, or if see blue, then delay, then must choose square.] The animal can accomplish this either by retaining the image of the stimulus [the red or the blue dots] or by having in their memory an image of what they will need to choose [the circle or the square.] The case of remembering the prior image is retrospective processing, and the anticipation of the forthcoming image is prospective processing.

Consider a visual delayed paired associate (DPA) task in which there are two sample objects (e.g., “S1” and “S2”) and two choice objects (“C1” and “C2”). If S1 is the sample, the animal must choose C1 after the delay, and if S2 is the sample, the animal must choose C2. Animals could solve this task by maintaining over the delay a memory of the samples (S1 or S2) or a memory of the anticipated choice stimuli (C1 or C2). The former (memories of events in the recent past) is called retrospective processing, and the latter (anticipation of future events) is called prospective processing (Roitblat, 1980; Honig and Thompson, 1982).

Prospective processing allows animals to optimize behavior by preparing in advance for critical events. They can, for example, act more quickly and direct attention to catch a fleeting event that might otherwise be missed.

In the experiment, two monkeys had sensors implanted to measure activity of certain neurons in the lateral prefrontal cortex (PF).

Some terms:

DPA: delayed paired associate task [like the S1/S2, C1/C2 task mentioned above.]

DMS: delayed match-to-sample [both the stimulus and the desired choice are the same image.]



Monkeys performed in alternate blocks DPA and DMS tasks.

(1) Monkey begins by grasping metal bar and fixate eyes on small spot for 2s.

(2) Then, a sample object is presented at the center of the gaze for 0.5s.

(3) Then there is a 1s delay.

(4) Then test object is displayed for 0.5s. If the test object matches the sample, the monkey is to release the metal bar within 0.5s in order to receive a juice reward. For DPA trials, there were prior months of training to associate the proper images.


There was increased activity in the neurons during delay periods. That activity increased as the test object appearance drew nearer.

Note that there is a marked increase in activity over the delay as the time of test object presentation approaches. Such “climbing activity” has been suggested to reflect prospective coding (Quintana and Fuster, 1992; Miller et al., 1996). [...] Although the monkey could not predict which sample would appear, it could predict when it would appear. This activity may reflect that expectation.

Gregor Rainer; S. Chenchal Rao; and Earl K. Miller. Prospective Coding for Objects in Primate Prefrontal Cortex. The Journal of Neuroscience, 1 July 1999, 19(13): 5493-5505.



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