Neural hybrid model of semantic object memory: Implications from event-related timing using fMRI

Abstract

Previous studies by our group have demonstrated fMRI signal changes and synchronized gamma rhythm EEG oscillations between thalamus and cortical regions as subjects recall objects from visually presented features. Here, we extend this work by estimating the time course of fMRI signal changes in the cortical and subcortical regions found to exhibit evidence for task-related activation. Our results indicate that there are separate loci of signal changes in the thalamus (dorsomedial and pulvinar) that exhibit notable differences in times of onset, peak and return to baseline of signal changes. The signal changes in the pulvinar demonstrate the slowest transients of all the cortical and subcortical regions we examined. Evaluation of cortical regions demonstrated salient differences as well, with the signal changes in Brodmann area 6 (BA6) rising, peaking, and returning to baseline earlier than those detected in other regions. We conclude that BA6 mediates early designation or refinement of search criteria, and that the pulvinar may be involved in the binding of feature stimuli for an integrated object memory.

The Semantic Object Retrieval Test (SORT) in Normal Aging and Alzheimer Disease

“…Successful task performance during functional magnetic resonance imaging (fMRI) was found to engage medial Brodmann area 6, bilateral ventral temporal lobe, and the dorsomedial and pulvinar nuclei of the left thalamus. 10,11 The task also has the added advantages of being brief and that it can be administered without specialized training.…”

An integrated neural model of semantic memory, lexical retrieval and category formation, based on a distributed feature representation

“…This aspect shares some ideas with the ''Neural Hybrid Model of semantic Object Memory'' by Hart et al (2007), Kraut et al (2003Kraut et al ( , 2004.…”

“…Finally, Hart and coworkers formulated a complex theory, which incorporates several previous aspects: Their model (named ''hybrid model of semantic object memory''), assumes that different cortical regions embody not only sensory-motor representations of objects, but also higher cognitive aspects (lexical, emotional,…). This information is then integrated by means of synchronized neural activity in the gamma-range modulated by the thalamus Kraut et al 2003Kraut et al , 2004.…”

Neuropsychological deficits after bithalamic hemorrhages

“…Global amnesia after thalamic stroke mostly requires bilateral lesions [10]. Mediodorsal thalamic nucleus is a likely candidate to cause this type of amnesia "per se" [11], or because of its connections to cortical areas and to the hippocampal formation [12][13][14]. In recent years, the importance of major fiber tracts that connect thalamus to medial temporal lobe structures to mnemonic function is stressed [10].…”