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Contralateral thalamic projections predominantly reach transitional cortices in the rhesus monkey
1Department of Health Sciences, Boston University, Massachusetts 02215.
The Journal of Comparative Neurology
|June 22, 1994
Summary
Contralateral thalamocortical projections, though less common than ipsilateral ones, are prevalent in olfactory and transitional cortices of rhesus monkeys. These crossed connections, unlike ipsilateral ones, depend more on cortical type than location, suggesting developmental persistence differences.
Area of Science:
- Neuroscience
- Comparative Anatomy
- Primate Brain Research
Background:
- Thalamocortical connections are typically ipsilateral, but contralateral projections exist in adult mammals.
- The specific targets and origins of contralateral thalamocortical projections remain unclear.
- Cortical types (transitional vs. eulaminate) in rhesus monkeys exhibit varying connectional patterns.
Purpose of the Study:
- To investigate whether contralateral thalamic projections target specific cortices, particularly olfactory and transitional prefrontal areas.
- To compare the prevalence of contralateral versus ipsilateral thalamic projections to different cortical regions in rhesus monkeys.
- To determine if contralateral projections originate from specific thalamic nuclei.
Main Methods:
- Utilized retrograde tracers to map thalamic projections in rhesus monkeys.
- Studied projections to primary olfactory, transitional orbital and medial cortices, and eulaminate cortices.
- Quantified and compared the number of labeled neurons in the contralateral and ipsilateral thalamus for each cortical area.
Main Results:
- Ipsilateral thalamic projection patterns varied based on cortical location (orbital, medial, olfactory).
- Contralateral projections were consistently found in midline, mediodorsal, anterior medial, and intralaminar thalamic nuclei.
- Contralateral projections primarily targeted olfactory and transitional cortices, rarely reaching eulaminate areas, with percentages ranging from 0-14% of ipsilateral projections.
Conclusions:
- Contralateral thalamocortical projections in rhesus monkeys are more dependent on cortical type than location.
- Olfactory and transitional cortices receive bilateral thalamic input, while eulaminate cortices receive predominantly ipsilateral input.
- Findings suggest differential persistence of contralateral thalamocortical interactions between transitional and eulaminate cortices into adulthood.