Miller looked at working memory in monkeys, he especially focused on the later PFC. He trained monkeys on a working memory task that required a successive coding of two stimulus attributes: identity and location. A sample stimulus is presented, then there is a 1 second delay then the objects are shown, one of which matches the sample. They must remember the position. He saw that there are three responses:
- "what" cells respond to specific objects, responses sustained over the delay period
- "where" selective to certain locations
- "what-where" cells respond to specific combo of what and where information
Recency Memory
Patients with frontal lobe lesions are impaired in the ability to organize and segregate events in memory. A recency task involving cards with 2 pictures are given to these patients. They are shown the cards and then are asked which object was most recently presented. People with frontal lobe damage did okay at the recognition task but are impaired at the recency task.
Source Memory
Source memory is about the context of the learning. Squire et al looked at patients with frontal lobe damage. He gave them and normal patients facts to learn. After 6-8 days of retention interval, they were tested. When they answered the questions correctly they were asked where they had learned the information. Patients with frontal lobe damage performed as well as controls on recall but made mistakes on the source task. Glisky et al looked at just healthy patients but he grouped them into high and low functioning frontal lobes. They listened to sentences about common events, half were read by a women the other half were read by a man. They tested item memory by reading them a novel sentence paired with the study sentences. They were asked which one they had heard and who had read it. The two frontal lobe groups did not differ on recall but did differ on source memory.
Prefrontal Cortex
Patients are given a series of pictures containing letters and squares at random location. They must remember the order of the instruction-relevant stimuli. If they had to remember the location of the squares activation is greater in the parietal and dorsal prefrontal regions. Remembering the letters caused greater activation in the temporal lobe and inferior frontal cortex of the left hemisphere.
- SPS: more activation for spatial
- IFG: ore activation for verbal
- APF: equal
- DLPF: pre activation when remembered backwards
In the n-back tests, patients needed to say which stimulus matched the stimulus n item ago. Activation in the lateral prefrontal cortex increases as the difficulty is increased.
Goal-Oriented Behavior
Wisconsin Card Sorting Task: cards vary along 3 dimensions: shape, color and numerosity. Participants had to sort the cards according to an experimenter-defined sorting rule. The experimenter says whether it is correct or incorrect after each card is played. After the participant has learned the rule, the experimenter will switch the rule again. Patients with frontal lobe lesions have difficulty with this task. They tend to perseverate, which is when they can not learn a new rule, they will apply the initial rule over and over.
Retrieval and Selection of Task Relevant Information
Art Shimamura: PFC can be conceptualized as a dynamic filtering. Focusing on what is important and filter out what is not relevant. Frontal lobes play a critical role in selecting task-relevant information. The stroop task is when colored words spell out color names. Name and colors to don match. Frontal lobe patients tend to have problems with this task.
Anterior Cingulate Gyrus
Operates as an executive attention system. Coordinates activity of others. Highest level of mental processes - it is the direct flow of traffic.
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