Thalamus has a role in human working memory

What is it about?

This study provided direct evidence for the role of a deep brain structure, thalamus, and specifically its mediodorsal nucleus, in human working memory. We studied patients with deep brain stimulator implanted in their thalamus for treatment of refractory epilepsy. High frequency electric stimulation temporarily disrupts the functioning of the deep brain target nucleus and thus allows for studying brain structure function relationship in humans. Turning high frequency electric stimulation repeatedly on and off while subjects are engaged in a cognitive task allows for online assessment of the role of a specific nucleus in a specific cognitive process. In this study we showed that turning high frequency electric stimulation at mediodorsal nucleus disrupted working memory performance but did not disrupt other cognitive processes such as response inhibition. On the other hand, high frequency electric stimulation at a nucleus next to mediodorsal nucleus i.e. anterior thalamic nuclei did not disrupt working memory performance. Thus, we showed that the impairment in working memory performance was not a general effect of deep brain stimulation independent of location but rather a specific finding at the mediodorsal nucleus. In conclusion, we provided direct causal evidence from humans for the role of mediodorsal nucleus of the thalamus in human working memory.

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Why is it important?

Previously, mediodorsal nucleus of thalamus has been linked in working memory in animal studies and in some human studies but there has not been direct causal evidence for its role in humans. The current findings are of importance in highlighting the importance of assessing cognitive effects of DBS treatment. DBS parameters can then be adjusted to minimize cognitive side effects along with optimal treatment effect. In current clinical practice there are still challenges in precise localization of the deep brain stimulation electrodes. With different thalamic nuclei having different roles in cognitive processes and being located in close proximity to one another assessing the impact of stimulation on different cognitive processes may give additional data points to imaging that will help in precise localization of the electrodes. Working memory deficits are common in many different developmental, neurological and psychiatric brain disorders as well as brain damage. Furthermore, working memory provides the basis for efficient cognitive functioning in daily life. Thus, working memory deficits are common and have important impact in cognitive functioning in daily life. Currently, there are no effective treatments available for working memory deficits. In search for treatments that will enhance cognition in patients with deficits in cognitive functions it is of outmost importance to get direct evidence for the brain structures involved in higher cognition in humans such as working memory.

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