Human mediodorsal thalamic nucleus as a potential target for deep brain stimulation: review of the literature and anatomical considerations

Discussion Anatomical and functional data The MDTN is the second largest nuclear aggregation located within the medial part of the thalamus and is closely related to the centromedian/parafascicular nucleus complex3. Distinct thalamic nuclei, like the MDTN and centromedian/parafascicular complex, are embedded in different basal ganglia-thalamocortical loops, which integrate cognitive and emotional aspects of human behaviour4. The human MDTN is in a crucial position that allows it to establish connections with diverse cerebral structures5. It is an association hub mediating interconnections mainly with the prefrontal cortex (major efferent projection)6,7. Tracer studies in primates and in vivo diffusion tensor tractography findings in both humans and monkeys confirm its role in relaying networks that connect to the dorsolateral prefrontal, orbitofrontal, frontal medial and cingulate cortices6. The MDTN has strong reciprocal connections with the dorsolateral prefrontal cortex, suggesting that the MDTN, like the dorsolateral prefrontal cortex, participates in higher cognitive functions such as spatial Abstract Introduction The dorsomedial or mediodorsal thalamic nucleus is embedded in different basal ganglia-thalamocortical loops, which integrate cognitive and emotional aspects of human behaviour. It is involved in several neuropsychiatric conditions. Mediodorsal thalamic nucleus deep brain stimulation has been repeatedly reported in animal models. The purpose of this article was to review critically the literature regarding basic science and clinical data of the mediodorsal thalamic nucleus, considering it as a potential deep brain stimulation target. Discussion The mediodorsal thalamic nucleus is an association hub mediating interconnections mainly with the prefrontal cortex. It has strong reciprocal connections with the dorsolateral prefrontal cortex, suggesting that it participates in higher cognitive functions such as spatial working memory. Specifically, schizophrenia is associated with volume and neuronal changes in the mediodorsal thalamic nucleus and pulvinar. In the mediodorsal thalamic nucleus of schizophrenic subjects, neuronal number is significantly lower and neuronal size is significantly smaller. The mediodorsal thalamic nucleus also plays the main role in amygdalo-hippocampal seizures and controls the limbic seizures. Experimental data showed that electrical stimulation of the mediodorsal thalamic nucleus elicits field potentials in several cortical areas of the frontal lobe. From an anatomical point of view, an electrode trajectory to the human mediodorsal thalamic nucleus is achievable without traumatising cortical vessels, the lateral ventricles or basal ganglia nuclei. Conclusion Treatment-resistant schizophrenia could theoretically be the most probable indication for such a minimally invasive intervention.