Effect of Mild Thyrotoxicosis on Performance and Brain Activations in a Working Memory Task

Abstract

AimsDisturbed levels of thyroid hormones are associated with neuropsychiatric disorders, including memory impairments. The aim of this study was to evaluate effects of mild induced thyrotoxicosis on working memory and its neural correlates.MethodsTwenty-nine healthy, male subjects with normal thyroid state participated in the study. Functional MRI was acquired during a working memory task (n-back task) before and after ingesting 250 μg L-thyroxin per day for a period of eight weeks. In addition, neuropsychological tests were performed.ResultsIn the hyperthyroid condition the subjects showed slower reaction times, but a higher accuracy in the 0-back version of the memory tasks. Fewer differences between euthyroid and hyperthyroid state were seen for the more difficult conditions of the n-back task. FMRI revealed effects of difficulty in the parahippocampal gyrus, supplementary motor area, prefrontal cortex, anterior cingulate cortex, posterior cerebellum, rolandic operculum and insula (p<0.05, FWE corrected). When comparing euthyroid and hyperthyroid condition in relation to task-induced activation, differences of activation were found in the right prefrontal cortex as well as in the right parahippocampal area. In the psychological assessment, the alerting effect in the Attention Network Task (ANT) and four out of five parameters of the auditory verbal learning test (AVLT) showed an increase from euthyroid to hyperthyroid state.ConclusionsIt can be concluded that even a short-term intake of thyroid hormones leads to an activation of brain areas associated with working memory and to an improvement of accuracy of working memory tasks.

Aberrant intra and inter network resting state functional connectivity in thyrotoxicosis

“…Our finding indicates reduced intra network FC in fronto‐parietal network regions, including frontal pole, middle frontal gyrus, inferior frontal gyrus, parietal operculum cortex, superior parietal lobule, supramarginal gyrus, in thyrotoxicosis patients compared to controls. The findings are in line with a previous task based functional study that showed impaired performance during the N‐back working memory task and altered BOLD activity in the prefrontal area, insula and parahippocampal regions in mild thyrotoxicosis . An earlier neuropsychological study also showed impairment in working memory, executive functions and attention in thyrotoxicosis.…”

“…In thyrotoxicosis, thyroid gland produces excessive amounts of fT3 and fT4, leading to a suppression of serum TSH. Patients with thyrotoxicosis suffer from various neurocognitive issues, such as prominent nervousness, depression, anxiety, irritability, poor concentration, memory impairment and a decline in executive functions . Until now, the underlying mechanisms of these neurocognitive alterations in thyrotoxicosis patients has remain unexplored.…”

“…Previous neuroimaging studies have shown morphological, functional, metabolite and perfusion weighted changes associated with thyrotoxicosis. A functional magnetic resonance imaging (fMRI) study using the N‐back working memory task revealed altered activation in brain regions such as the parahippocampal gyrus, supplementary motor area, prefrontal cortex, anterior cingulate cortex, posterior cerebellum, rolandic operculum and insula in thyrotoxicosis . Similarly, an earlier resting state network FC study in thyrotoxicosis patients reported weak FC strength between the hippocampus and bilateral anterior cingulate cortex, posterior cingulate cortex and right medial orbitofrontal cortex using hippocampus as the seed region .…”

Mild Thyrotoxicosis Leads to Brain Perfusion Changes: An Arterial Spin Labelling Study

“…Both neuroimaging studies and clinical evidence suggest a role of the cerebellum in cognitive processes . In previous studies, we were able to show that thyroid hormones have an effect on structure and function of the cerebellum . Animal studies show that the cerebellum is involved in the production of thyroid hormones and expression of thyroid hormone receptors .…”

“…Numerous behavioural alterations have been described in patients with hypo‐ and hyperthyroidism . Only recently were these changes demonstrated to be supported by structural and functional brain changes . Particularly, the impact of thyroid hormone on memory functions has been shown not only using classical memory testing tasks , but also when testing for morphological changes .…”