Exploring anterior thalamus functional connectivity with cortical regions in prospective memory with ultra-high-field fMRI

Abstract

AbstractProspective memory, or memory for future intentions, engages particular cortical regions. Lesion studies also implicate the thalamus, with prospective memory deterioration following thalamic stroke. Neuroimaging, anatomical, and lesion studies suggest the anterior nuclei of the thalamus (ANT) in particular are involved in episodic memory, with electrophysiological studies suggesting an active role in selecting neural assemblies underlying particular memory traces. Here we hypothesized that the ANT are engaged in realizing prospectively-encoded intentions, detectable using ultra-high field strength functional MRI. Using a within-subject design, participants (N = 14; age 20-35 years) performed an ongoing n-back working memory task with two cognitive loads, each with and without a prospective memory component, during 7-Tesla functional MRI. Seed-to-voxel whole brain functional connectivity analyses were performed to establish whether including a prospective memory component in an ongoing task results in greater connectivity between ANT and cortical regions known to be engaged in prospective memory. Repeated measures ANOVAs were applied to behavioral and connectivity measures, with the factorsTask Type(with prospective memory or not) andN-Back(2-back or 3-back). Response accuracy was greater and reaction times faster without the prospective memory component, and accuracy was higher in the 2- than 3-back condition. We observed a main effect ofTask Typeon connectivity with an ANT seed, with greater ANT–DLPFC (dorsolateral prefrontal cortex) and ANT–STG (superior temporal gyrus) connectivity when including a prospective memory component. Post hoc testing based on a significant interaction showed greater ANT–DLPFC connectivity (p-FWE = 0.007) when prospective memory was included with the low and ANT–STG connectivity (p-FWE = 0.019) with the high cognitive load ongoing task. These locations showed no main effect ofN-Back. Connectivity based on a dorsomedial nucleus of the thalamus (DMNT) seed did not differ according toTask Typeat these locations. Enhanced connectivity between the ANT and the DLPFC, a brain region with an established role in strategic monitoring for prospective memory cues, arose with a low cognitive load ongoing task that enabled monitoring. This pattern was absent on directly increasing the cognitive load of the ongoing task without prospective memory, suggesting specificity for prospective memory. Greater ANT–STG connectivity on prospective memory inclusion in the higher cognitive load ongoing task condition fits with reports of STG activation on prospective memory through spontaneous retrieval. Differing connectivity based on a DMNT seed suggests ANT specificity. The findings fit with a coordinating role for the ANT in prospective remembering.