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The recognition memory deficit caused by mediodorsal thalamic lesion in non-human primates: a comparison with rhinal
A Parker1, M J Eacott, D Gaffan
1Department of Experimental Psychology, University of Oxford, UK.
Abstract:
Two earlier studies found that rhinal cortex ablations in the monkey (Macaca fascicularis) impaired delayed matching-to-sample (DMS) when the stimuli in the experiment came from a large population of possible stimuli, but not when the stimulus population was small, while uncinate fascicle section had no effect on DMS whatever the stimulus population size. The mediodorsal thalamus receives a large projection from the rhinal cortex, and has been implicated in recognition memory performance. We trained monkeys preoperatively in delayed matching-to-sample with large and small stimulus populations, exactly as in the earlier studies, then examined the effect of bilaterally ablating the medial portion of the mediodorsal thalamic nucleus. Mediodorsal lesion impaired postoperative delayed matching-to-sample performance with a large stimulus set, but had no effect on performance of DMS with a small stimulus population. In comparison with the earlier data from rhinal cortex lesions with the same methods, wherever a deficit was seen in the rhinal-lesioned animals the mediodorsal thalamic nucleus-lesioned animals showed a smaller deficit. We conclude that other efferents from the rhinal cortex, possibly those to the adjacent inferior temporal cortex, enable better performance in the mediodorsal thalamic nucleus-lesioned animals than in the animals with rhinal cortex ablation.
Insights
Ablating the mediodorsal thalamus in monkeys impaired recognition memory (delayed matching-to-sample) with large stimulus sets but not small ones. This suggests the rhinal cortex uses other pathways for recognition memory.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Primate Models
Background:
- Previous studies linked rhinal cortex ablations to deficits in delayed matching-to-sample (DMS) with large stimulus sets.
- Uncinate fascicle lesions did not affect DMS performance regardless of stimulus set size.
- The mediodorsal thalamus, a target of rhinal cortex projections, is implicated in recognition memory.
Purpose of the Study:
- To investigate the role of the mediodorsal thalamus in recognition memory.
- To compare the effects of mediodorsal thalamic lesions with prior rhinal cortex lesion data.
Main Methods:
- Monkeys (Macaca fascicularis) were trained on DMS with large and small stimulus populations.
- Bilateral ablations of the medial mediodorsal thalamic nucleus were performed.
- Postoperative DMS performance was assessed using both large and small stimulus sets.
Main Results:
- Mediodorsal thalamic lesions impaired DMS performance significantly with large stimulus sets.
- No significant impairment in DMS performance was observed with small stimulus populations.
- Deficits in mediodorsal thalamus-lesioned animals were less severe than those in rhinal cortex-lesioned animals.
Conclusions:
- The mediodorsal thalamus plays a role in recognition memory, particularly with complex stimulus sets.
- The rhinal cortex likely utilizes additional pathways, potentially to the inferior temporal cortex, to support recognition memory.
- These findings highlight the distinct yet interconnected roles of the rhinal cortex and mediodorsal thalamus in memory processes.