Role of the frontal lobes in memory

Question 1

Neuropsychological study (predates functional imaging)

• Tested memory of patients with frontal lobe lesions for previously learned facts, and when they had been learned
• Good memory for the facts themselves but poor memory for when they had been learned
• Suggests frontal lobes may be critical for recollecting the context in which events are previously experienced

Answer 1

Janowsky et al 1989

Question 2

Neuropsychological study

• Frontal patients are prarticularly impaired if stimuli are presented in a disordered fashion at encoding, or if there is significant interference between the stimuli to be recalled.

Answer 2

Incisa Della Rochetta and Milner 1993

Question 3

Functional neuroimaging

Sorted activity at encoding dependening on whether stimuli were subsequently remembered or forgotten

• Activity in left VLPFC and MTL at encoding predicted later successful remembering

Answer 3

Wagner et al 1998

Question 4

• Cued participants to perform one of two elaborative encoding tasks on words.- then asked them to recollect which encoding task they had carried out on each stimulus
• Activity in left VLPFC and hippocampus at encoding predicted subsequent successful recollection. (i.e. source memory)
• Activity in left perirhinal cortex predicted whether words were subsequently recognised as familiar (recognition memory- old or new?)

Answer 4

Davachi et al 2003

Question 5

• Activation of frontal regions during encoding tasks tends to be lateralised according to the type of stimuli involved.
• Left VLPFC and MTL were engaged more than right during the encoding of words
• Bilateral involvement for nameable objects
• Predominantly right hemisphere activation for unfamiliar faces (cant name- have to rely on visual info)

Answer 5

Kelley et al 1998

Question 6

Evidence that different sub-regions of VLPFC might support different kinds of elaborative processing.

• Greater activity associated with semantic and phonological elaboration were observed in anterior and posterior VLPFC, repectively

Answer 6

Poldrack et al 1999

Question 7

Among the first to demonstrate that organising material at encoding (e.g. into categories) can have a considerable impact on subsequent recall

Answer 7

Segal and Mandler 1967

Question 8

fMRI

• One aspect: studied cue specification- hypothesises that such a process would be involved more during recollection than familiarity (latter being a more automatic process) as well as during semantic analysis
• Activation confirming this pattern was seen in left VLPFC
• Found a region of posterior VLPC was active not only during semantic analysis but also during recollection and familiarity- suggests a role in the mainetnenace of information retrieved from long term memory.

Answer 8

Dobbins et al 2002

Question 9

Used event-related fMRI to contrast recollection of two forms of contextual information:

• Decisions one had previously made about stimuli (task memory)
• Which of two temporarily discint lists those stimuli had been presented in (list memoty)

Also test phase manipulation: recollection cue specifying the type of contextual detail to be retrieved on each trial was followed by wither a previously studied target stimulus (in which case would expect that a retrieval search would be undertaken) or a control stimulus (would not provoke occurrence of retrieval search). Hypothesis: if anterior pfc is involved in preretrieval processes, then activation would be expected both during trials in which both cue and target stimulus are presented, and during cue-only trials. If anterior PFC plays a role in retrieval search or postretreival monitoring of recovered info, activation would not be predicted during trials in which target stimuli are not present.

Results:

• Anterior prefrontal cortex responded significantly more during recollection of task than list context details.
• Activation profiles for lateral and medial aspects of anterior prefrontal cortex suggested differing roles in recognition.
• Lateral regions seem to be more involved in early retrieval stages of recoellection: lateral PFC activation was associated with readiness for a task memory judgement compared with a list memory judgement, irrespective of whether retrieval searches were actually undertaken.
• Medial regions contributing to later stages (e.g. monitoring and verification) : time-course data revlealed tahat signal in this region peakerd significantly later in the recollection process than did the response in lateral anterior PFC. Also was activated when target stimli were presented during the recollection of previous judgments about stimu, . Was also activated duering the study phase.
• ‘These results suggest that the anterior PFC plays an important role in recollection but that this role may be just one examples of a more general information processing capacity.’*

Answer 9

Simons et al 2005

Question 10

Tested free recall in patients with different kinds of frontal lobe lesions.

• Repetition errors occured most in patietns with right DLPFC damage.
• Suggests role for this ergion in monitoring/ checking of information.

Answer 10

Stuss et al 1994

Question 11

2 studies suggesting rolr for DLPFC in monitoring/checking of retrieval information

• 1) Showed greater DLFC activity during free than cued recall
• 2) Greater DLPFC activity during recodnition responses associated with low confidence

Answer 11

1) Fletcher et al 1998b
2) Henson et al 2000b

Question 12

fMRI study of 12 healthy volunteers.

• Tested hypothesis that one role of the right PFC is to monitor the info retrieved in episodic memory in order to make an appropriate response.
• • Critical comparison was between two word recognition tasks that differed only in whether correct responses did or did not require reference to the spatiotemporal context of words presented during a previous study episode.
• Observed activation in the same right DLPFC region identified in Fletcher et al 1998b, Henson et al 2000b associated with increased contextual monitoring demands.
• More ventral region of right PFC shoused retrieval-related activation that was independent of task instructions.

Answer 12

Henson et al 1999

Question 13

fMRI. Compared 2 different recollection tasks

Within –subjects fMRI design, to examine two reality monitoring conditions:

• memory for perceived vs imagined stimuli
• memory for participant vs experimenter performed operations

Results:

• Task that involved consideration of whther the participant of another person had previously read out a word was associated with activation in medial APFC and right DLPFC.
• Sole difference between two reality monitoring tasks was greater activation in medial anterior prefrontal cortex when recollecting on participant vs experimenter compared to perceived vs imagined.
• Authors note that this region has previously been linked with attending to mental states.
• Task differences were also reflected in greater functional connectivity between the two regions during the self/experimenter recollection context.

‘This indicates a role for medial anterior PFC in the monitoring of retrieved info relation to internal or external aspects of context.

• Finally, related brain activity to measures of proneness to psychosis and schizotypal traits. Significant correlations between reduced medial APFC signal and scores on such measures.

Answer 13

Simons et al 2008