Yunqing Li1, Prasanna Karunanayaka1, and Qing X Yang1,2
1Radiology, Penn State College of Medicine, Hershey, PA, United States, 2Neurosurgery, Penn State College of Medicine, Hershey, PA, United States
Synopsis
The contributions of distinct anatomical brain
regions within the medial temporal lobe (MTL) during successful learning and recognition is poorly understood. In this research, we attempt to unravel how the MTL brain
structures interact and integrate information during successful memory recall
under different conditions during the performance of a face-name fMRI task.Purpose
It remains unclear
whether distinct anatomical brain regions within the medial temporal lobe (MTL)
subserve different functional roles during successful memory encoding and retrieval
(1-5). In order to address this gap in current knowledge, we designed an fMRI
experiment to investigate the neural basis of associative memory processes
during face and name linking. Our approach was to compare and contrast successful-recall
and failed–recall in order to delineate brain regions in the MTL that make
distinct functional contributions during face-name associative memory
formation.
Methods
Subjects: Twenty
(10 females; age range= 21–45 yrs; mean age = 31yrs) participated in the study
with informed consent.
fMRI Paradigm: All participants
completed a block design, face-name learning and recognition fMRI paradigm. The
face-name task included 16 faces (8 male) and 64 face-name pairs. During the 16 s encoding trials, a face-name pair
was presented on a LCD screen. During the 16 s retrieving (or recognition)
trials, a face was presented with 4 names on a LCD screen. A 48 s distractor period, alternating
between “+” and “0” was included after each encoding trial (Figure 1). During recognition trials, participants were
asked to indicate with a button press which name was associated with the face
during the learning (or encoding) phase. Participants were presented with face-name
pairs during each learning block and similarly, 4 face-name pairs during each
recognition block.
Equipment and
scanning parameters: fMR images were acquired with
a 3T Siemens Trio and 8 channel head coil with a T2*-weighted
gradient-echo EPI sequence with the following parameters: TR/TE/FA = 2000ms/30ms/90
deg; FOV = 240 mm× 240mm; Matrix size = 80 ×
80; # of axial slices=35; slice thickness = 4 mm; # of repetitions = 174.
Data analysis: fMRI data were
processed using SPM8 (Wellcome Trust Centre for Neuroimageing). Activation maps
were generated using the General Linear Model (GLM). A block was deemed a success
(S) if all four face names were recalled correctly. All other blocks were
marked as failed-recall blocks (F). The distractor period was taken as the baseline
block (B). Subject wise contrast maps were generated for each experimental
condition, i.e., learning or recall, the S-block or the F-block in comparison
to the B-block. Group-level maps were then generated using a second level
random effects analysis.
Results
Significantly higher activations were detected in the right posterior
hippocampal formation (P < 0.0043), left anterior hippocampus (p < 0.0133),
left amgydala (p < 0.0207), left perirhinal (p < 0.0272), right
parahippocampus (p < 0.0066) during the S-Block when compared to the F-block
(Figure 2). The fMRI % signal change in the left posterior
hippocampus during the experiment showed a rapid decrease for each block of
learing and recognition (Figure
3).
Discussion
Our results highlight
that no medial temporal lobe (MTL) structure can independently process and
perform the cross-domain association memory demands of face-name associations.
This process seems to be highly dynamic when quantified in terms of the BOLD
signal time-course in respective brain structures. Taken together, these
results suggest an intricate interaction between MTL structures for learning
and recognition memory manipulations in the human brain. In turn, this will
help ask new questions about human memory formation that were not feasible
before.
Acknowledgements
The study was supported by the Department of Radiology at Penn State, George M. Leader Foundation and a grant from the U.S.
National Institute of Aging, R01-AG027771References
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