Memory Processes in the Right and Left Rhinal Cortex
Objective: Human neuropsychological and neurofunctional imaging studies have highlighted the importance of the medial temporal lobes in declarative memory and suggested material-specific lateralization with greater left medial temporal lobe involvement for verbal material and greater right medial temporal lobe involvement for non-verbal material. However the respective role of the different structures which make up the medial temporal lobe is poorly understood. Here, we study the role of the left and right rhinal cortices (anterior subhippocampal structures) in memory formation and recognition using intracerebral electrophysiological recordings.
Methods: Ten patients, with drug-refractory unilateral medial temporal lobe epilepsy were implanted with depth electrodes in the rhinal cortices (left side, n=5, right side). The procedure comprised 4 old/new blocks of words presented visually and 4 old/new blocks of abstract figures, each divided in an encoding (15 targets), an interfering and a recognition phase (the 15 targets among 30 trial-unique distracters). During the interfering phases, the patients were asked to discriminate colors of abstract figures in the verbal blocks or to provide the gender of words in the abstract figure blocks. The abstract figures were chosen for their difficulty to be verbalized. Event-related potentials (ERPs) were recorded during the three phases of the experiment.
Results: Mean accuracy was 85% correct responses for patients in the verbal and figure tasks; two patient was at chance level in the figure tasks. An asymmetry depending on the material processed was identified. In the right rhinal cortex, abstract figures elicited a large or double negativity peaking around 220 and 400 ms mean latency during the encoding as well as the recognition phases. On the contrary, only a single component culminating around 220 ms was observed for the color discrimination interfering phase. The same pattern of ERPs with significantly lower amplitude however was recorded in response to words. The reverse pattern was observed in the left rhinal cortex, words eliciting a large negativity culminating between 300 and 400 msec while weaker components were recorded in response to figures. Only one component at 220 ms was recorded in the gender of words interfering task.
Discussion: The physiological activation of verbal and non-verbal recognition begins by a first component (N220) which could correspond to visual perceptual processing, more pronounced on the right side. The subsequent N400 can be referred to as the AMTL-N400 and appears more specific for mnesic processes. The particular contribution of rhinal cortices to recognition memory is discussed as a function of hemispheric lateralization as well as with respect to the organization of medial temporal lobe structures.
Conference:
10th International Conference on Cognitive Neuroscience, Bodrum, Türkiye, 1 Sep - 5 Sep, 2008.
Presentation Type:
Oral Presentation
Topic:
Abstracts
Citation:
Chauvel
P and
Liegeois Chauvel
C
(2008). Memory Processes in the Right and Left Rhinal Cortex.
Conference Abstract:
10th International Conference on Cognitive Neuroscience.
doi: 10.3389/conf.neuro.09.2009.01.023
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Received:
27 Nov 2008;
Published Online:
27 Nov 2008.
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Correspondence:
Patrick Chauvel, INSERM U 751, Marseilles, France, Patrick.Chauvel@mail.ap-hm.fr