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Reeders, P. C.

Publications and source records attributed to Reeders, P. C..

2 recordsLinked to original sources
bioRxiv2022

Identifying the midline thalamus in humans in vivo

The midline thalamus is essential to flexible cognition, memory, and stress regulation and its dysfunction is associated with several neurological and mental health disorders including Alzheimers disease, schizophrenia, and depression. Despite the pervasive role of the midline thalamus in cognition and disease, almost nothing is known about it in humans due to the lack of a rigorous methodology for finding this brain region using noninvasive imaging technologies. Here, we introduce a new method for identifying the midline thalamus in vivo using probabilistic tractography and k-means clustering with diffusion weighted imaging data. This method clusters thalamic voxels based on data-driven cortical and subcortical connectivity profiles, and then segments midline thalamic nuclei based on connectivity profiles established in rodent and macaque tracer studies. Results from two different diffusion weighted imaging sets, including adult data (22-35yrs) from the Human Connectome Project (n=127) and adolescent data (9-14yrs) collected at Florida International University (n=34) showed that this approach reliably classifies midline thalamic clusters. As expected, these clusters were most evident along the dorsal/ventral extent of the third ventricle and primarily connected to the agranular medial prefrontal cortex (e.g., anterior cingulate cortex), nucleus accumbens, and medial temporal lobe regions. The midline thalamic clusters were then bisected based on a human brain atlas (Ding et al., 2016) into a dorsal midline thalamic cluster (paraventricular and paratenial nuclei) and a ventral midline thalamic cluster (rhomboid and reuniens nuclei). This anatomical connectivity-based identification procedure for the midline thalamus offers new opportunities to study this region in vivo in healthy populations and in those with psychiatric and neurological disorders. Significance StatementThe midline thalamus is essential for flexible cognition, decision making, and stress regulation. Abnormal development, dysfunction, and neurodegeneration of the midline thalamus is thought to be a critical pathology in several psychiatric and neurological disorders. Yet, little is known about the role of the human midline thalamus. Here we solve the problem of localization in vivo by using probabilistic tractography and data driven clustering (k-means), a method capable of capitalizing on known connectivity in non-human animal tracer studies. Localizing the midline thalamus based on its connectivity patterns provides a useful tool for future functional and structural human MRI studies to investigate clinical implications of the midline thalamus in diseases such as Alzheimers and schizophrenia.

neuroscience↗
bioRxiv2018

Hippocampus activations reflect temporal contexts while medial prefrontal cortex activations reflect ordinal positions during sequence memory in humans

Remembering sequences of events defines episodic memory, but retrieval can be driven by both ordinality and temporal contexts. Whether these modes of retrieval operate at the same time or not remains unclear. Theoretically, medial prefrontal cortex (mPFC) confers ordinality, while the hippocampus (HC) associates events in gradually changing temporal contexts. Here, we looked for evidence of each with BOLD fMRI in a sequence task that taxes both retrieval modes. To test ordinal modes, items were transferred between sequences but retained their position (e.g., AB3). Ordinal modes activated mPFC, but not HC. To test temporal contexts, we examined items that skipped ahead across lag distances (e.g., ABD). HC, but not mPFC, tracked temporal contexts. There was a mPFC and HC by retrieval mode interaction. These current results suggest that the mPFC and HC are concurrently engaged in different retrieval modes in support of remembering when an event occurred. Significance StatementMemory for sequences of events is a defining aspect of everyday episodic memory allowing our brain to separate unique experiences that otherwise have overlapping sensory and spatial content. Sequence memory is impaired in typical aging and in disorders such as Alzheimers disease. The results of the current study provide new evidence that two retrieval modes concurrently arise during sequence memory, and they have distinct neural correlates. The medial prefrontal cortex contributes to an ordinal retrieval mode, while at the same time, the hippocampus contributes a gradually-changing temporal context mode of retrieval. These data shed new light on why typical episodic memory requires both the medial prefrontal cortex and the hippocampus, and suggests a functional dissociation between the medial prefrontal cortex and hippocampus across these modes of retrieval.

neuroscience↗