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Published on: November 11, 2011
A case of polymicrogyria in macaque monkey: impact on anatomy and function of the motor system
Eric Schmidlin1, Christophe Jouffrais, Patrick Freund
1Unit of Physiology and Program in Neurosciences, Department of Medicine, Faculty of Sciences, University of Fribourg, Chemin du Musée 5, CH-1700 Fribourg, Switzerland. eric.schmidlin@unifr.ch
Background:
Polymicrogyria is a malformation of the cerebral cortex often resulting in epilepsy or mental retardation. It remains unclear whether this pathology affects the structure and function of the corticospinal (CS) system. The anatomy and histology of the brain of one macaque monkey exhibiting a spontaneous polymicrogyria (PMG monkey) were examined and compared to the brain of normal monkeys. The CS tract was labelled by injecting a neuronal tracer (BDA) unilaterally in a region where low intensity electrical microstimulation elicited contralateral hand movements (presumably the primary motor cortex in the PMG monkey).
Results:
The examination of the brain showed a large number of microgyri at macro- and microscopic levels, covering mainly the frontoparietal regions. The layered cortical organization was locally disrupted and the number of SMI-32 stained pyramidal neurons in the cortical layer III of the presumed motor cortex was reduced. We compared the distribution of labelled CS axons in the PMG monkey at spinal cervical level C5. The cumulated length of CS axon arbors in the spinal grey matter was not significantly different in the PMG monkey. In the red nucleus, numerous neurons presented large vesicles. We also assessed its motor performances by comparing its capacity to execute a complex reach and grasp behavioral task. The PMG monkey exhibited an increase of reaction time without any modification of other motor parameters, an observation in line with a normal CS tract organisation.
Conclusion:
In spite of substantial cortical malformations in the frontal and parietal lobes, the PMG monkey exhibits surprisingly normal structure and function of the corticospinal system.
Insights
Polymicrogyria, a brain malformation, surprisingly did not impair the corticospinal system's structure or function in a macaque monkey. Motor performance showed subtle changes, indicating resilience despite cortical abnormalities.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Primate Neuroanatomy
Background:
- Polymicrogyria is a cortical malformation linked to epilepsy and cognitive deficits.
- The impact of polymicrogyria on the corticospinal (CS) system is not well understood.
- This study investigated the CS tract in a macaque with spontaneous polymicrogyria.
Observation:
- The polymicrogyria affected frontoparietal regions with disrupted cortical organization.
- Reduced pyramidal neurons were observed in the motor cortex of the affected monkey.
- CS tract axonal arbors in the spinal cord and red nucleus structure were analyzed.
Findings:
- Despite cortical malformations, the CS tract's axonal organization in the spinal cord remained comparable to normal monkeys.
- The polymicrogyria monkey showed increased reaction time in a complex motor task but no other significant motor deficits.
- The red nucleus exhibited neuronal changes, including large vesicles.
Implications:
- The corticospinal system demonstrates remarkable resilience to significant polymicrogyria.
- These findings suggest potential compensatory mechanisms within the primate brain.
- Further research can explore therapeutic strategies for neurological disorders with cortical malformations.
