Biology subjects

McAndrews, M. P.

Publications and source records attributed to McAndrews, M. P..

5 recordsLinked to original sources

bioRxiv2024

Subjective salience ratings are a reliable proxy for physiological measures of arousal

Pain is an inherently salient multidimensional experience that signals potential bodily threats and promotes nocifensive behaviours. Any stimulus can be salient depending on its features and context. This poses a challenge in delineating pain-specific processes in the brain, rather than salience-driven activity. It is thus essential to salience match control (innocuous) stimuli and noxious stimuli, to remove salience effects, when aiming to delineate pain-specific mechanisms. Previous studies have salience-matched either through subjective salience ratings or the skin conductance response (SCR). The construct of salience is not intuitive, and thus matching through self-report poses challenges. SCR is used as a proxy measure that captures physiological arousal, which overcomes the nebulous construct of salience. However, SCR cannot be used to salience-match in real-time (i.e., during an experiment) and assumes an association between salience and physiological arousal elicited by painful and non-painful stimuli, but this has not been explicitly tested. To determine whether salience and physiological arousal are associated, thirty-five healthy adults experienced 30 heat pain and 30 non-painful electric stimuli of varying intensities. Stimuli were subjectively matched for salience and SCR was measured to each presentation. A linear mixed model found no differences in SCR between salience-matched heat and electric stimuli. A mediation analysis showed that salience fully mediated the relationship between stimulus intensity and SCR (proportion mediated=83%). In conclusion, salience and physiological arousal are associated, and subjective salience ratings are a suitable for salience-matching pain with non-painful stimuli. Future work can thus use subjective salience ratings to delineate pain-specific processes.

neuroscience↗

bioRxiv2023

Single voxel autocorrelation reflects hippocampal function in temporal lobe epilepsy

We have previously shown that autocorrelation analyses of BOLD signal applied to single voxels in healthy controls can identify behaviorally-relevant gradients of temporal dynamics throughout the hippocampal long-axis. A question that remains is how changes in the brains functional and structural integrity affect single voxel autocorrelation. In this study we investigate how hippocampal autocorrelation is affected by hippocampal dysfunction by investigating a population of patients with unilateral temporal lobe epilepsy (TLE). Many patients with TLE have mesial temporal sclerosis (MTS), characterized by scarring and neuronal loss particularly in the anterior hippocampus. Here we compared patients with left and right TLE, some with and without MTS, to healthy controls. We applied our single voxel autocorrelation method and data-driven clustering approach to segment the hippocampus based on the autocorrelation of resting state fMRI. We found that patients with left TLE had longer intrinsic timescales (i.e., higher autocorrelation) compared to controls, particularly in the anterior-medial portion of the hippocampus. This was true for both the epileptogenic and non-epileptogenic hemispheres. We also evaluated the extent of cluster preservation (i.e., spatial overlap with controls) of patient autocorrelation clusters and the relationship to verbal and visuospatial memory. We found that patients with greater cluster preservation in the anterior-medial hippocampus had better memory performance. Surprisingly, we did not find any effect of MTS on single voxel autocorrelation, despite the structural changes associated with the condition. These results suggest that spatiotemporal dynamics of activity can be informative regarding the functional integrity of the hippocampus in TLE.

neuroscience↗

bioRxiv2022

Leveraging the resting brain to predict memory decline after temporal lobectomy

ObjectivesAnterior temporal lobectomy as a treatment for temporal lobe epilepsy is associated with a variable degree of postoperative memory decline, and estimating this decline for individual patients is a critical step of preoperative planning. Presently, predicting memory morbidity relies on indices of preoperative temporal lobe structural and functional integrity. However, epilepsy is increasingly understood as a network disorder, and memory a network phenomenon. We aimed to assess the utility of functional network measures to predict postoperative memory changes. MethodsPatients with left and right temporal lobe epilepsy (TLE) were recruited from an epilepsy clinic. Patients underwent preoperative resting-state fMRI (rs-fMRI) and pre- and postoperative neuropsychological assessment approximately one year after surgery. We compared functional connectivity throughout the memory network of each patient to a healthy control template based on 19 individuals to identify differences in global organization. A second metric indicated the degree of integration of the to-be-resected temporal lobe with the rest of the memory network. We included these measures in a linear regression model alongside standard clinical and demographic variables as predictors of memory change after surgery. ResultsSeventy-two adults with TLE were included in this study (37 left/35 right). Left TLE patients with more abnormal memory networks, and with greater functional integration of the to-be-resected region with the rest of the memory network preoperatively, experienced the greatest decline in verbal memory after surgery. Together, these two measures explained 44% of variance in verbal memory change (F(2,31)=12.01, p=0.0001), outperforming standard clinical and demographic variables. None of the variables examined in this study were associated with visuospatial memory change in patients with right TLE. ConclusionResting-state connectivity provides valuable information concerning both the integrity of to-be-resected tissue as well as functional reserve across memory-relevant regions outside of the to-be-resected tissue. Intrinsic functional connectivity has the potential to be useful for clinical decision-making regarding memory outcomes in left TLE, and more work is needed to identify the factors responsible for differences seen in right TLE.

neuroscience↗

bioRxiv2020

Schemas provide a scaffold for neocortical integration at the cost of memory specificity over time

Memory transformation is increasingly acknowledged in theoretical accounts of systems consolidation, yet how memory quality and neural representation change over time and how schemas influence this process remains unclear. In this fMRI study, participants encoded and retrieved schema-congruent and incongruent object-scene pairs using a paradigm that probed coarse and detailed memories over 10-minutes and 72-hours. When a congruent schema was available, details were lost over time as representations were integrated in the medial prefrontal cortex (mPFC), and enhanced post-encoding coupling between the anterior hippocampus and mPFC was associated with coarser memories. Over time, pattern similarity in the hippocampus changed such that the posterior hippocampus represented specific details and the anterior hippocampus represented the general context of specific memories, irrespective of congruency. Our findings suggest schemas are used as a scaffold for accelerated consolidation of congruent information, and illustrate change in hippocampal organization of detailed contextual memory over time.

neuroscience↗

bioRxiv2020

Resting-State Functional Connectivity Predicts Individual Pain Ratings to a Tonic Orofacial Pain Stimulus

Pain is a subjective experience with significant individual differences. Laboratory studies investigating pain thresholds and experimental acute pain have identified structural and functional neural correlates. However, these types of pain stimuli have limited ecological validity to real-life pain experiences. Here, we use an orthodontic procedure--the insertion of an elastomeric separator between teeth--which typically induces mild to moderate pain that peaks within 2 days and lasts several days. We aimed to determine whether the baseline structure and resting-state functional connectivity (rsFC) of key regions along the trigeminal nociceptive and pain modulatory pathways correlate with subsequent peak pain ratings. Twenty-six healthy individuals underwent structural and resting-state functional (rs-fMRI) scanning prior to the placement of a separator between the first and second molars, which was kept in place for five days. Participants recorded pain ratings three times daily on a 100-mm visual analogue scale. Peak pain was not significantly correlated with diffusion metrics of the trigeminal nerve, or grey matter volume of any brain region. Peak pain did, however, positively correlate with baseline rsFC between the thalamus contralateral to the separator and bilateral insula, and negatively correlated with connectivity between the periaqueductal gray (PAG) and core nodes of the default mode network (medial prefrontal and posterior cingulate cortices). The ascending (thalamic) nociceptive and the descending (PAG) pain modulatory pathways at baseline each explained unique variation in peak pain intensity ratings. In sum, pre-interventional functional neural architecture of both systems determined the individual pain experience to a subsequent ecologically valid pain stimulus.

neuroscience↗