Poorer white matter microstructure predicts slower and more variable reaction time performance: evidence for the neural noise hypothesis in a large lifespan cohort

Most prior research in the neural and behavioral sciences has been focused on characterizing averages in cognition, brain characteristics, or behavior, and attempting to predict differences in these averages among individuals. However, this overwhelming focus on mean levels may leave us with an incomplete picture of what drives individual differences in behavioral phenotypes by ignoring the variability of behavior around an individual’s mean. In particular, better white matter (WM) structural microstructure has been hypothesized to support consistent behavioral performance by decreasing gaussian noise in signal transfer. In contrast, lower indices of white matter microstructure have been associated with greater within-subject variance in the ability to deploy performance-related resources, especially in clinical samples. We tested this ‘neural noise’ hypothesis in a large adult lifespan cohort (Cam-CAN) with over 2500 individuals in a (2681 behavioral sessions with 708 scans in adults aged 18–102) using measures of WM tract microstructure to predict mean levels and variability in reaction time performance on a simple behavioral task using a dynamic structural equation model (DSEM). We found broad support for neural noise hypothesis, such that lower WM microstructure predicted individual differences in separable components of behavioral performance estimated using DSEM, including slower mean responses and increased variability. These effects were robust when including age in the model, suggesting consistent effects of WM microstructure across the adult lifespan above and beyond concurrent effects of ageing. Crucially, these results demonstrate the utility of DSEM for modeling and predicting behavioral variability directly, and the promise of studying variability for understanding cognitive processes.

Facial Trustworthiness Perceptions Across the Adult Lifespan

This paper adopted an adult lifespan developmental approach by asking 87 young (25-39 years), 59 middle-aged (44-59 years), and 47 older (60-78 years) women and men to rate the trustworthiness of faces that systematically varied in age (young, middle-aged, older) and emotion (neutral, happy, sad, fearful, angry, disgusted) from the FACES Lifespan Database.

Pronoun production remains stable over the adult lifespan for contexts with topic continuity

A prevalent finding in the referential communication literature is that older adults produce more ambiguous pronouns than younger adults, likely because they have difficulty determining the prominence of referents. This finding has been widely understood to reflect a general age-related deficit in communication. However, all studies from this line of work have used materials involving topic shifts (i.e. when the to-be-named referent shifts from one character to another, which requires perspective-taking and can be cognitively costly). To determine the extent to which younger and older adults’ pronominal use diverges, we investigated whether other aspects of the discourse context influence age-related differences in referential choice, apart from topic shifts. Here we tested a large sample of adults (N=496, ages 18-82) using narrative elicitation tasks across four experiments and nine contexts of topic continuity (i.e. contexts in which the to-be-named referent remained the same). In Experiments 1 and 2, we varied the number of characters in the scene while keeping the sex/gender of the characters distinct and found that pronominal use did not differ by age for scenes with 1, 2, and 3 characters. In Experiments 3 and 4, we varied the number of characters, the sex/gender of those characters (such that they were the same or different), and the linguistic emphasis placed on the main character. Again, we found no age differences across all conditions. Taken together, our findings suggest that older adults’ difficulty with prominence estimates is not all- encompassing, but rather appears to be confined to contexts involving topic shifts.

Morris Water Maze and Contextual Fear Conditioning Tasks to Evaluate Cognitive Functions Associated With Adult Hippocampal Neurogenesis

New neurons are continuously generated and functionally integrated into the dentate gyrus (DG) network during the adult lifespan of most mammals. The hippocampus is a crucial structure for spatial learning and memory, and the addition of new neurons into the DG circuitry of rodents seems to be a key element for these processes to occur. The Morris water maze (MWM) and contextual fear conditioning (CFC) are among the most commonly used hippocampus-dependent behavioral tasks to study episodic-like learning and memory in rodents. While the functional contribution of adult hippocampal neurogenesis (AHN) through these paradigms has been widely addressed, results have generated controversial findings. In this review, we analyze and discuss possible factors in the experimental methods that could explain the inconsistent results among AHN studies; moreover, we provide specific suggestions for the design of more sensitive protocols to assess AHN-mediated learning and memory functions.

Atypically slow processing of faces and non-faces in older autistic adults

Face recognition is a fundamental function that requires holistic processing. Differences in face processing have been consistently identified in autistic children, but it is unknown whether these differences persist across the adult lifespan. Using event-related functional magnetic resonance imaging, we measured holistic face processing with a rapid Mooney faces task in 50 autistic and 49 non-autistic participants (30–74 years). Behavioral tasks included a self-paced version of the same paradigm and a global–local processing task (Navon). Reduced detection rates for faces, but not non-faces, were found in autistic adults, including slower responses on all conditions. Without time constraints, differences in accuracy disappeared between groups, although reaction times in correctly identifying faces remained higher in autistic adults. The functional magnetic resonance imaging results showed lower activation in the left and right superior frontal gyrus in the autism group but no age-related differences. Overall, our findings point toward slower information processing speed rather than a face recognition deficit in autistic adults. This suggests that face-processing differences are not a core feature of autism across the adult lifespan. Lay abstract Some theories suggested that social difficulties in autism arise from differences in the processing of faces. If face-processing difficulties are central to autism, then they should be as persistent as social difficulties across the lifespan. We tested this by asking autistic and neurotypical participants between 30 and 75 years to complete face detection tasks. Both autistic and neurotypical adults responded more slowly with age. When participants had to respond quickly, autistic adults made more errors in face detection regardless of their age. However, when the time constraint was removed, autistic adults performed as well as the neurotypical group. Across tasks, autistic adults responded more slowly when asked to detect both face and non-face stimuli. We also investigated brain activation differences in the face detection task with functional magnetic resonance imaging. The results indicated lower activation in the autism group in the left and right superior frontal gyrus. The superior frontal gyrus is not typically implicated in face processing but in more general processing, for example, keeping instructions in mind and following them. Together with the behavioral results, this suggests that there is no specific deficit in face processing in autistic adults between 30 and 75 years. Instead, the results suggest differences in general processing, particularly in the speed of processing. However, this needs to be investigated further with methods that are more sensitive to the timing of brain activation.