The featured paper is ‘Medial Prefrontal Cortex Plays A Critical And Selective Role in ‘Feeling of Knowing’ Meta-Memory Judgements’ by Modirrousta and Fellows.
The authors begin by briefly discussing the general role of the frontal cortex and then focus on the medial prefrontal cortex citing evidence that supports its role in performance monitoring and also in the ‘default mode of brain function’. The authors tentatively link performance monitoring with the concept of self-monitoring of learning and memory and discuss the operationalisation of meta-memory. They also introduce the term judgement-of-learning (JOL) which describes the monitoring that occurs during acquisition and retention of memories. The authors discuss two other types of meta-memory – retrospective confidence judgements (RCJ) – how confident is a person that they have remembered something correctly and feeling of knowing (FOK) – how confident is a person that they will recognise the correct response. The authors then go onto discuss how much remains to be discovered in this area. For instance they look at evidence suggesting how cues can interact with these constructs in different ways. They also look at how neuropsychological studies have helped make inroads into understanding these concepts and cite clinical evidence suggestive of frontal lobe involvement from findings in Korsakoff’s syndrome. They then cite other evidence suggesting the relevance of the frontal lobes to the constructs described earlier.
The aim in this study was to examine the relationship between the medial prefrontal cortex and the three constructs mentioned above. The authors aimed to do this using a case series where people in the study had identified lesions in the Dorsal Anterior Cingulate Cortex (ACC). Other areas were also involved and the authors argue that these were not random (presumably relating to cerebrovascular lesions which occur in the territories of particular blood vessels and which therefore determine the distribution).
Firstly this was a small study with only 5 participants. All had been recruited from a research database, they had all experienced strokes involving either the anterior cerebral artery of the peri-callosal artery territory and the average age of the group was 59 years. There were 19 age and education matched controls and no significant difference between the average of the groups on the American version of the National Adult Reading Test.
Subjects were presented with a face-name episodic memory task (24 faces presented in blocks of 6) with free recall and recognition being tested. They rated each of JOL, RCJ and FOK. There was a 1 minute delay distraction test with face-name pairs during which RCJ was assessed. There was a second component to the experiment in which the delay period was increased and only 3 of the people with mPFC lesions participated in this stage of the experiment. Data was analysed using the primary measure of the Goodman-Kruskal gamma index which looks at the variation between two variables and secondary analyses of between group comparisons using t-Tests and ANOVA.
In Experiment 1 with one level of difficulty, both groups performed better on recognition than on recall with the latter not differing significantly between the groups. Subjects with mPFC damage performed significantly worse than controls on recognition although performing better than chance. JOL – as measured by difference between predicted and actual recall accuracy were similar in both groups. However on measures of RCJ and FOK the mPFC group performed significantly worse than the controls. Interestingly the control group scored higher for meta-memory on tasks where they responded correctly while this pattern was not seen in the people with mPFC lesions. When performance on memory was controlled for, there was no difference between the groups. In the task however both groups produced low scores on the FOK even when they gave correct scores. In the second stage of the experiment there was no difference between the groups on meta-memory measures on the more difficult tasks. When the easier memory test was performed again, the mPFC group still performed significantly worse on the FOK task.
The authors conclude that as they didn’t find significant group differences on the JOL task, and there is previous evidence for frontal lobe involvement in JOL, that it involves a non-mPFC area of the frontal lobes. As JOL was intact when FOK was impaired the authors suggest this shows that the two are independent. mPFC damage was associated impairment in RCJ and FOK judgements although they point out that the latter remained in the easier memory task while disappearing on the more difficult one. They suggest that either right or left mPFC damage or dorsal mPFC damage can interfere with FOK. The authors argue that there is a case for cues playing a role in meta-memory from the current experimental results.
There are some difficulties I have with the results however. There is a small sample size. While the inter-group comparisons have produced significant findings there are only 5 patients, who are effectively being treated as a homogenous group. Within this group though there are four areas where there is an overlap of lesion areas, the mPFC being present in all 5. Perhaps it could be argued that as the groups are being compared, and that as only this area is affected it will account for the between group differences. Nevertheless due to the small sample size, how do we know that bilateral versus unilateral lesions don’t play a big difference? This wasn’t tested in this study norin my opinion could it be meaningfully. Furthermore, the American version of the NART was used although this will be testing premorbid IQ. What would be more interesting to see is whether this group had other differences in their psychometric profile. For instance we know that there are various types of mild cognitive impairment including vascular MCI – did the group fall into this category. We also know that diabetes, blood pressure and medication can affect memory and yet there was no information in this regards. There are some clear conclusions from this study that are easily testable and it will be interesting to see the results of larger replication studies and to see how this relates to the construct of Mild Cognitive Impairment.
Steps to Treatment = 6 (Larger study to replicate findings, use findings to create valid model, use model to inform treatment approaches, trial informed treatments, meta-analysis of treatment trials, if successful incorporate into policy)
Modirrousta M and Fellows L.K. Medial Prefrontal Cortex Plays A Critical And Selective Role in ‘Feeling of Knowing’ Meta-Memory Judgements’. Neuropsychologia. 46. 2008. 2958-2965.
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