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Does retrieving decades-old spatial memories activate the medial temporal lobes less than retrieving recently acquired spatial memories?
NeuroImage
II,
Number
5, 2000,
Part 2
of
2 parts 10
E bl@
MEMORY
- LEARNING
Does Retrieving Decades-old Spatial Memories Activate the Medial Temporal Lobes Less than Retrieving Recently Acquired Spatial Memories? A.R. Mayes*, C.E. Mackay?, D. Montaldi*,
J.J. DownesS, K.D. Singht, N. Roberts?
*Section of Clinical Neurology, University of Shefield, Shefield, UK. ?Magnetic Resonance and Image Analysis Centre (MARIARC), University Liverpool, UK.
of Liverpool.
$Department of Psychology, University of Liverpool, Liverpool, UK. Although it is widely agreed that the hippocampus and other medial temporal lobe (MTL) structures are initially involved in the storage of fact and event information, there is disagreement about whether memories for these kinds of information continue to depend on the MTL for storage regardless of how old and well rehearsed the memories are. On the one hand. it has heen argued that the MTLs continue to mediate fact and event memories (1). On the other hand, it has been argued that as such memorie\ age and are rehearsed, storage and retrieval gradually cease to be mediated by the MTLs and become the responsibility of the neocortex (2). If this latter view is correct, then retrieval of very old memories should activate the MTLs less than retrieval of similar, recently acquired memories. This study examined whether this prediction is fulfilled when subjects retrieve old and new route memories. Spatial memory retrieval was used because it has been argued that this activates the hippocampus, and, as hippocampally-focused activations have rarely been reported, we wished to check that the claim was true (3). Method Prior to scanning the spouses of subjects were interviewed to provide cues that would elicit route recall of specific routes from two different time periods in the subjects lives. “Old” routes which had been learnt and well-used 40 years previously by the subject and not re-used since, and “New” routes which had been learnt and well-used within the last 6 months. Subjects were not informed of the nature of the memory task until immediately preceding the scan. They were then told that on visual presentation of a particular cue they were to generate the route from their house at that time, to the place identified by the cue (e.g., Grandma’s house, conference centre). These two retrieval tasks “Old routes” and “New routes” were contrasted with a low-level baseline in which subjects had to count backwards from a number presented to them on the screen. Each cue (or number) was presented for 15 seconds and subjects were instructed to fill the time with the appropriate task. A 1.5T LX/Nvi Nemo-Optimised MR imaging system (General Electric, Milwaukee, USA) was used to acquire 22 contiguous T2* weighted gradient-echo EPI images (TE = 40ms, TR = 3s. flip angle = 900, matrix = 64x64, field of view = 22, slice thickness = 5mm). Slices were oriented parallel to the AC-PC line and covered the entire cerebrum. The design involved one functional run per subject, consisting of 150 EPI volume acquisition5 and divided into 30 epochs each of 15 seconds. The three conditions were presented in a random order. (The design for one subject differed slightly. They were scanned over three runs providing the New vs Old, New vs counting backwards and Old vs counting backwards contrasts across the runs rather than wihin a run). Data were motion corrected and spatially normalised to a template brain before group analysis. Functional data were analysed using SPM99 software (http://www.til.ion.ucl.ac.uk). Results Compared to the low-level baseline, as did the retrieval of New routes (x the retrieval of New routes. A direct a right hippocampal activation (x =
the retrieval of Old = 27, y= -39 z= contrast of the Old 21, y = -12, z =
routes produced a right hippocampal activation (x ~ 22. y -16. / L -131 -12 ). The retrieval of Old routes however, activated this rcpion mom than and New routes confirmed thi\ since the Old-New contrast also produced -15).
Discussion The results confirm that retrieval of spatial memories activates the hippocampus relative to a lowlevel baseline. Retrieval ot o!(! spatial route memories which had not been recently rehearsed produced more hippocampal acti\ ation than the rctricv ai 01 I ec~~i~:l. acquired memories. ‘This occurred although the memory conditions were matched for amount anil kind of inf~~rn:,iti~~n : <‘ti gt.5\‘\I While these results provide no support for the view that the MTLs are only rnvolvcd with +itiul i-enievdl dnd +oi;rgc ior ;J lillll(r~. time, they do not refute this view. This is because the retrieval\ in the scanner were late1 well remembered \o whdt \+‘I\ ijenl; retrieved was also being encoded into episodic memory. To control for this encoding confound, future Lvork must e.~annnt’ !t ncrn~~ re-encoding old and new spatial memories produces equivalent hippocampal activations, References 1. Nadel, L. 6t Moscovitch, M (1997) Current Opinions in Neurobiology 2. Squire, L.R. & Alvarez. P. (1995) Current Opinions in Neurobiology 3. Maguire, E.A. et al. (1998) Science. 280, 921-924.
S421
7. 217-227 5, 169-177.
II,
Number
5, 2000,
Part 2
of
2 parts 10
E bl@
MEMORY
- LEARNING
Does Retrieving Decades-old Spatial Memories Activate the Medial Temporal Lobes Less than Retrieving Recently Acquired Spatial Memories? A.R. Mayes*, C.E. Mackay?, D. Montaldi*,
J.J. DownesS, K.D. Singht, N. Roberts?
*Section of Clinical Neurology, University of Shefield, Shefield, UK. ?Magnetic Resonance and Image Analysis Centre (MARIARC), University Liverpool, UK.
of Liverpool.
$Department of Psychology, University of Liverpool, Liverpool, UK. Although it is widely agreed that the hippocampus and other medial temporal lobe (MTL) structures are initially involved in the storage of fact and event information, there is disagreement about whether memories for these kinds of information continue to depend on the MTL for storage regardless of how old and well rehearsed the memories are. On the one hand. it has heen argued that the MTLs continue to mediate fact and event memories (1). On the other hand, it has been argued that as such memorie\ age and are rehearsed, storage and retrieval gradually cease to be mediated by the MTLs and become the responsibility of the neocortex (2). If this latter view is correct, then retrieval of very old memories should activate the MTLs less than retrieval of similar, recently acquired memories. This study examined whether this prediction is fulfilled when subjects retrieve old and new route memories. Spatial memory retrieval was used because it has been argued that this activates the hippocampus, and, as hippocampally-focused activations have rarely been reported, we wished to check that the claim was true (3). Method Prior to scanning the spouses of subjects were interviewed to provide cues that would elicit route recall of specific routes from two different time periods in the subjects lives. “Old” routes which had been learnt and well-used 40 years previously by the subject and not re-used since, and “New” routes which had been learnt and well-used within the last 6 months. Subjects were not informed of the nature of the memory task until immediately preceding the scan. They were then told that on visual presentation of a particular cue they were to generate the route from their house at that time, to the place identified by the cue (e.g., Grandma’s house, conference centre). These two retrieval tasks “Old routes” and “New routes” were contrasted with a low-level baseline in which subjects had to count backwards from a number presented to them on the screen. Each cue (or number) was presented for 15 seconds and subjects were instructed to fill the time with the appropriate task. A 1.5T LX/Nvi Nemo-Optimised MR imaging system (General Electric, Milwaukee, USA) was used to acquire 22 contiguous T2* weighted gradient-echo EPI images (TE = 40ms, TR = 3s. flip angle = 900, matrix = 64x64, field of view = 22, slice thickness = 5mm). Slices were oriented parallel to the AC-PC line and covered the entire cerebrum. The design involved one functional run per subject, consisting of 150 EPI volume acquisition5 and divided into 30 epochs each of 15 seconds. The three conditions were presented in a random order. (The design for one subject differed slightly. They were scanned over three runs providing the New vs Old, New vs counting backwards and Old vs counting backwards contrasts across the runs rather than wihin a run). Data were motion corrected and spatially normalised to a template brain before group analysis. Functional data were analysed using SPM99 software (http://www.til.ion.ucl.ac.uk). Results Compared to the low-level baseline, as did the retrieval of New routes (x the retrieval of New routes. A direct a right hippocampal activation (x =
the retrieval of Old = 27, y= -39 z= contrast of the Old 21, y = -12, z =
routes produced a right hippocampal activation (x ~ 22. y -16. / L -131 -12 ). The retrieval of Old routes however, activated this rcpion mom than and New routes confirmed thi\ since the Old-New contrast also produced -15).
Discussion The results confirm that retrieval of spatial memories activates the hippocampus relative to a lowlevel baseline. Retrieval ot o!(! spatial route memories which had not been recently rehearsed produced more hippocampal acti\ ation than the rctricv ai 01 I ec~~i~:l. acquired memories. ‘This occurred although the memory conditions were matched for amount anil kind of inf~~rn:,iti~~n : <‘ti gt.5\‘\I While these results provide no support for the view that the MTLs are only rnvolvcd with +itiul i-enievdl dnd +oi;rgc ior ;J lillll(r~. time, they do not refute this view. This is because the retrieval\ in the scanner were late1 well remembered \o whdt \+‘I\ ijenl; retrieved was also being encoded into episodic memory. To control for this encoding confound, future Lvork must e.~annnt’ !t ncrn~~ re-encoding old and new spatial memories produces equivalent hippocampal activations, References 1. Nadel, L. 6t Moscovitch, M (1997) Current Opinions in Neurobiology 2. Squire, L.R. & Alvarez. P. (1995) Current Opinions in Neurobiology 3. Maguire, E.A. et al. (1998) Science. 280, 921-924.
S421
7. 217-227 5, 169-177.