Cognitive and White-Matter Compartment Models Reveal Selective Relations between Corticospinal Tract Microstructure and Simple Reaction Time

Abstract

The speed of motor reaction to an external stimulus varies substantially between individuals and is slowed in aging. However, the neuroanatomical origins of interindividual variability in reaction time (RT) remain unclear. Here, we combined a cognitive model of RT and a biophysical compartment model of diffusion-weighted MRI (DWI) to characterize the relationship between RT and microstructure of the corticospinal tract (CST) and the optic radiation (OR), the primary motor output and visual input pathways associated with visual-motor responses. We fitted an accumulator model of RT to 46 female human participants' behavioral performance in a simple reaction time task. The non-decision time parameter ( T er ) derived from the model was used to account for the latencies of stimulus encoding and action initiation. From multi-shell DWI data, we quantified tissue microstructure of the CST and OR with the neurite orientation dispersion and density imaging (NODDI) model as well as the conventional diffusion tensor imaging model. Using novel skeletonization and segmentation approaches, we showed that DWI-based microstructure metrics varied substantially along CST and OR. The T er of individual participants was negatively correlated with the NODDI measure of the neurite density in the bilateral superior CST. Further, we found no significant correlation between the microstructural measures and mean RT. Thus, our findings suggest a link between interindividual differences in sensorimotor speed and selective microstructural properties in white-matter tracts. SIGNIFICANCE STATEMENT How does our brain structure contribute to our speed to react? Here, we provided anatomically specific evidence that interindividual differences in response speed is associated with white-matter microstructure. Using a cognitive model of reaction time (RT), we estimated the non-decision time, as an index of the latencies of stimulus encoding and action initiation, during a simple reaction time task. Using an advanced microstructural model for diffusion MRI, we estimated the tissue properties and their variations along the corticospinal tract and optic radiation. We found significant location-specific correlations between the microstructural measures and the model-derived parameter of non-decision time but not mean RT. These results highlight the neuroanatomical signature of interindividual variability in response speed along the sensorimotor pathways.

Tract-defined regional white matter hyperintensities and memory

“…We add to this body of work by confirming that not only that macrostructural damage to association tracts, but also projection tracts, have a role in memory function. Our unexpected finding regarding the relationship between WMH in projection white matter tracts, particularly the relationship between corticospinal tract and memory, deviates from previous DTI studies, which suggested a role of the corticospinal tract in sensorimotor functions rather than cognitive functions (Carter et al., 2012; Karahan et al., 2019). A plausible explanation of the relationship between corticospinal tract WMH and memory may simply be due to the tract's proximity to the lateral ventricles, where periventricular WMH reside and are known to be associated to memory (Munoz Maniega et al., 2019; Smith et al., 2011).…”

White Matter Hyperintensities Related to Parkinson's Disease Executive Function

“…Studies have shown lower CST integrity to be associated with worse perceptual speed in persons with older age, 57 but also higher neurite density in the CST to be associated with faster nondecision time in reaction time tasks, implying a more efficient network for voluntary actions. 58 In persons with relapsing-remitting multiple sclerosis, Riccitelli et al determined that lesions in the CST and FM are associated with poor SDMT performance. 59 Studies in patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy have shown that damage of the left CST is associated with poor processing speed.…”

Breaking Deadlocks: Reward Probability and Spontaneous Preference Shape Voluntary Decisions and Electrophysiological Signals in Humans

“…The accumulation process terminates when the activation of any accumulator reaches a response threshold B (B > A) and the choice corresponding to the winning accumulator is selected. The model prediction of RT (measured in seconds) is the sum of the duration of the accumulation process and a constant nondecision time T er , with the latter accounting for the latency associated with other processes including stimulus encoding and action execution (Brown and Heathcote 2008;Nunez et al 2019;Karahan et al 2019).…”

“…During perceptual learning, the accumulation rate increases along with behavioral improvements (Jia et al 2018), while the non-decision time remains unchanged in the late stage of training (Zhang and Rowe 2014). Furthermore, the accumulation rate is associated with the individual differences in working memory (Schmiedek et al 2007) and attention (Nunez et al 2017), while the non-decision time is faster in individuals with higher diffusion MRI-derived neurite density in the corticospinal tract, the primary motor output pathway (Karahan et al 2019). Recent research showed that both parameters can be influenced by reward magnitude (Wagner et al 2020), and the current study will examine further whether reward probability and preference influence the two model parameters.…”