Structural connectivity of the anterior temporal lobe impacts semantic retrieval efficiency
Poster No:
1091
Submission Type:
Abstract Submission
Authors:
Nicolas Deom1, Omar Khalil2, Irene Giannoylis2, Mary Pat McAndrews2
Institutions:
1University of Toronto, Toronto, MT, 2Krembil Research Institute, Toronto, Ontario
First Author:
Co-Author(s):
Introduction:
Semantic memory is the term usually used to describe the sum of all conceptual knowledge an individual possesses. Knowledge about unique entities, usually denoted with proper nouns, is thought to involve integration of many specific bits of information, and accessing these unique concepts is thought to rely on a network of ventrotemporal regions with a key hub in the left anterior temporal lobe (ATL). Individuals with left temporal lobe epilepsy (TLE) have particular difficulty with proper name retrieval, but the unique contribution of white-matter tracts, which connect this hub to the rest of the network, to this impairment remains an open question. Here, we examine the hypothesis that abnormalities in key tracts in TLE patients will impact successful retrieval of these concepts.
Methods:
We recruited a sample of 26 left TLE patients being investigated for surgery and 17 healthy controls. Participants performed a semantic decision task where they were presented with a cue word (e.g., Jennifer Aniston) and two target words (e.g.,Brad Pitt and George Clooney) and had to select which of the two targets was more closely related to the cue (Brad Pitt being the expected answer here). Diffusion-weighted images were acquired on a 3T Signa MR system. Standard preprocessing operations were applied on the collected data, using the fMRIPrep pipeline. Tract reconstruction of the left and right uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF), as well as all analyses were performed using TRACULA, running on Freesurfer 7.4.1. We compared mean fractional anisotropy (FA) and FA voxel-by-voxel along the tract between patients and controls. We also examined the relationship between mean FA and performance on the semantic task. Significant clusters in the along-the-tract analysis were considered significant at p<0.05 FWE-corrected. Mean FA comparisons of whole tracts were considered significant at p<0.05.
Results:
Patients overall showed worse performance on the behavioral task than the healthy controls, suggesting they have more difficulty retrieving information about unique entities. Comparing mean FA values between the groups showed greater asymmetry in the ILF in left TLE group compared to healthy controls, where the left TLE group had significantly lower FA in their left ILF compared to their right while the controls showed no asymmetry. There was no significant difference for the UF. In the voxel-wise analyses, there was a significant cluster in the frontal-lobe section of the left UF, where patients had significantly lower FA than controls. No cluster reached significance in the other three tracts considered. In patients, reduced mean FA in the left ILF was associated with poorer task performance, while reduced mean FA in the left UF was associated with a less cautious approach (faster reaction time, but poorer accuracy).
Conclusions:
We found that FA in the left ILF and UF, as a measure of white-matter tract integrity, was reduced in TLE. For TLE patients, having lower FA in the left ILF was also related to a reduced ability to retrieve semantic information about unique entities. The impact of structural damage or dysfunction in the anterior temporal hub on this process is well-established in the literature. Our findings add to the newer literature indicating that retrieval of information about unique semantic entities is also related to the integrity of long-ranging temporooccipital connections.
Disorders of the Nervous System:
Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s) 2
Learning and Memory:
Long-Term Memory (Episodic and Semantic) 1
Modeling and Analysis Methods:
Diffusion MRI Modeling and Analysis
Keywords:
Epilepsy
Memory
WHITE MATTER IMAGING - DTI, HARDI, DSI, ETC
Other - Semantic Memory
1|2Indicates the priority used for review
Provide references using author date format
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