Although it is well established that thalamic lesions may lead to profound amnesia, the precise contributionof thalamic sub-regions to memory remains unclear. In an influential article Aggleton andBrown proposed that recognition memory depends on two processes supported by distinct thalamic andcortical structures. Familiarity is mediated by the mediodorsal (MD) thalamic nucleus and the entorhinal/perirhinal cortex. Recollection ismediated by the anterior thalamic nucleus (AN), the mamillothalamictract (MTT) and the hippocampus. The authors also suggested that the lateral dorsal nucleus (LD) maycontribute to the thalamic/hippocampus system, thereby implying that the LD may play a role in recollection.Given the finding that material specific amnesia can occur following thalamic lesions, we testedan extension of the Aggleton and Brown model. We predicted that patients with bilateral lesions with abias to the left or right MD or AN/MTT/LD may exhibit impaired familiarity or recollection on verbal ornon-verbal memoranda.We report two patients with highly focal thalamic lesions and profound memory impairments affectingverbal and non-verbal memoranda. For the first time, diffusion-weighted imaging was employed toperform tractography of the MTT along with high-resolution anatomical MRI and detailed assessments ofverbal and non-verbal memory. Our data support only some aspects of the Aggleton and Brown model.Both patients had leftMD nucleus and AN/MTT lesions and performed poorly on familiarity and recall forverbal memoranda, just as predicted by the model. However, both patients’ performance for non-verbalmemoranda (human faces and topography) is more difficult to reconcile with the model. Patient 1 haddamage to the right AN/MTT/LD with sparing of the MD: familiarity should therefore have been preservedbutwas not. Patient 2 had damage to the rightMDwith sparing of AN/MTT: recollection should have beenpreserved but was not. This finding raises the possibility that fractionation of familiarity and recollectionto separate thalamic nuclei may not fully capture the role of thalamic sub-regions in memory function.© 2008 Elsevier Ltd. All rights reserved.
|Number of pages||14|
|Publication status||Published - 2008|
All Science Journal Classification (ASJC) codes
- Experimental and Cognitive Psychology
- Cognitive Neuroscience
- Behavioral Neuroscience