James B. Brewer, Zuo Zhao, John D Desmond, Gary H. Glover, John D. E. Gabrieli

Making Memories: Brain Activity That Predicts How Well Visual Experience Will Be Remembered

Thomas Pierce

Brain damage studies have shown that the medial temporal lobe (MTL) is important for declarative memory, with damage here leading to amnesia.

These studies do not tell us about the specific role in memories (encoding, storage, retrieval).

Some preliminary fMRI studies have show that MTL is more active during exposure to novel scenes, suggesting a role in encoding. Primarily in the parahippocampal cortex (part of MTL) High activation in the frontal cortex, as well.

This activation could be explained many ways (E.g. signifying encoding process, novelty response, etc.), which is why the following experiment was carried out, to determine what this activation really meant.

Introduction

6 normal, right handed subjects, 3 were females. Ages 22-32

4 fMRI scans (4 different slices of the brain)

Show participants 24 images of colored indoor and outdoor scenes, asked to determine whether images were indoors oroutdoors.

30 minutes later, they gave a memory test to participants: Show all 96 previous images with 32 completely new

pictures Ask them to indicate whether they had seen the images Responses were: Well remembered, familiar, forgotten

(or hadn’t actually seen)

Experimental Task

Images: Remembered: 25% (range 5-47%) Familiar: 27% (17-38%) Forgot 48% (25-66%) Remembered pictures varied

between participants

fMRI showed that there were 7 specific areas that had correlated activity with the 3 different answers (I.e. Activation during viewing of picture matched answer certainty). Several other areas activated, but seemingly uncorrelated. 6 were in bilateral parahippocampal cortex (PHC) 1 in right inferior frontal sulcal region of dorsolateral prefrontal cortex

(DLPFC)

Results

A-C - Average signal magnitude greater than resting activation for each brain area. D – Mean activation of PHC

Results

Degree of right DLPFC and PHC activation seems to predict how strong a declarative memory will be.

Right DLPFC has been previously linked to spatial working memory, PHC with long term memory

Evidence for a proposed neural circuit between right DLPFC and PHC that is important for the creation of spatial long term memory. Some kind of relation between the two areas that works to create long

term visuospatial memory

Lateralized long term memory encoding processes

Discussion

While the overall idea of the paper was of merit, and results could have been very interesting, the execution failed, resulting in a paper I do not fully trust.

Primary problems: Small sample size of 6 Only very specific areas of brain studied Poor organization (few sub-titles, much information was in References

and Notes) Confusing, not well defined terminology. (E.g. The word remembered) Short discussion that didn’t make many implications (which would be

of limited validity anyways).

Suggestions for future research: Do it again, with a larger sample size, while examining more brain areas. After that, attempt similar studies with different memory processes (e.g. not visuospatial).

Opinion

Introduction: Medial temporal lobe associated with declarative memory, in particular the parahippocampal cortex (PHC). Frontal cortex is, as well.

Experiment: Examine PHC and dorsolateral prefrontal cortex (DLPFC) via fMRI while participants look at pictures. Test memory of pictures later. Look at correlation between activation in these areas versus how well pictures were remembered.

Results: Activation in PHC and right DLPFC strongly related to how well visual images remembered.

Discussion: Some kind of relation between PHC and right DLPFC that works to create long term visualspatial memory. There exists some lateralization for processes encoding memories.

Opinion: Not up to par.

Summary

Brewer, J.B., Zhao, Z., Desmond, J.E., Glover, G.H., & Gabrieli, J.D.(1998). Making memories: brain activity that predicts how well visual experience will be remembered. Science, 281, 1185-1187.

Citation

Questions?