Biology subjects

Flournoy, J. C.

Publications and source records attributed to Flournoy, J. C..

3 recordsLinked to original sources

bioRxiv2021

Graded variation in cortical T1w/T2w myelination during adolescence

Myelination influences brain connectivity during sensitive periods of development by enhancing neural signaling speed and regulating synapse formation to reduce plasticity. However, in vivo studies characterizing the maturational timing of cortical myelination during human development remain scant. Here, we take advantage of recent advances in high-resolution cortical T1w/T2w myelin mapping methods, including principled correction of B1+ transmit field effects, using data from the Human Connectome Project in Development (N=628, ages 8-21) to characterize the maturational timing of myelination from childhood through early adulthood throughout the cerebral neocortex. We apply Bayesian spline models and functional latent clustering analysis to demonstrate graded variation in the rate of cortical T1w/T2w myelin growth in neocortical areas that is strongly correlated with the sensorimotor-association (S-A) axis of cortical organization reported by others. In sensorimotor areas T1w/T2w myelin starts at high levels at early ages, increases at a fast pace, and decelerates at later ages (18-21). In intermediate multimodal areas along the S-A axis, T1w/T2w myelin tends to start at intermediate levels and increase linearly at an intermediate pace. In transmodal/paralimbic association areas high along the S-A axis, T1w/T2w myelin tends to start at low levels and increase linearly at the slowest pace. These data provide evidence for graded variation along the S-A axis in the rate of cortical myelination during adolescence, which could reflect ongoing plasticity underlying the development of complex information processing and psychological functioning. Significance StatementMyelin is a lipid membrane that is essential to healthy brain function. Myelin wraps axons to increase neural signaling speed, enabling complex neuronal functioning underlying learning and cognition. Here we characterize the developmental timing of myelination across the cerebral cortex during adolescence using recent advances in non-invasive myelin mapping. Our results provide new evidence demonstrating graded variation across the cortex in the timing of myelination during adolescence, with rapid myelination in lower-order sensory areas and gradual myelination in higher-order association areas. This spatial pattern of microstructural brain development closely parallels the sensorimotor-to-association axis of cortical organization and plasticity during ontogeny.

neuroscience↗

bioRxiv2019

Feeling left out or just surprised? Neural correlates of social exclusion and expectancy violations in adolescence

Social belonging and affiliation are important human drives that impact decision-making and health outcomes. While neural responses to social exclusion are increasingly well-characterized, studies rarely identify whether these responses reflect the affective distress or expectancy violation associated with exclusion. The present study compares neural responses to exclusion and over-inclusion, a similarly unexpected social occurrence that violates fair play expectations, but does not involve rejection, with a focus on implications for models of dorsal anterior cingulate cortex (dACC) function. In an fMRI adaptation of the Cyberball paradigm with human adolescents 11.1-17.7 years of age (N=69), we employed parametric modulators to examine scaling of neural signal with cumulative exclusion and inclusion events. The use of parametric modulators overcomes arbitrary definitions of condition onsets and offsets imposed on fluid, continuous gameplay. In support of the notion that the dACC plays a role in processing affective distress, this region exhibited greater signal with cumulative exclusion than cumulative inclusion events. However, this difference was partly driven by diminished signal accompanying cumulative inclusion, a finding that does not conform to either affective distress or expectancy violation model predictions. Additionally, we found that signal in the insula and dorsomedial prefrontal cortex scaled uniquely with social exclusion and over-inclusion, respectively, while conjunction analyses revealed that the rostromedial prefrontal cortex and left intraparietal sulcus responded similarly to both conditions. These findings shed light on which neural regions may exhibit patterns of differential sensitivity to exclusion or over-inclusion, as well as those that are more broadly engaged by both types of social interaction.

neuroscience↗

bioRxiv2019

Affective reactivity during adolescence: Associations with age, puberty and testosterone

Adolescence is a period of heightened social engagement that is accompanied by normative changes in neural reactivity to affective stimuli. It is also a period of concurrent endocrine and physical changes associated with puberty. A growing body of research suggests that hormonal shifts during adolescence impact brain development, but minimal research in humans has examined the relationship between intra-individual changes in puberty and brain function. The current study examines linear and nonlinear changes in affective reactivity in a longitudinal sample of 82 adolescents who underwent three fMRI sessions between the ages of 9 and 18 years. Changes in response to affective facial stimuli were related to age, pubertal stage, and testosterone levels. Using multilevel modelling, we highlight extensive nonlinear development of socio-emotional responsivity across the brain. Results include mid-pubertal peaks in amygdala and hippocampus response to fearful expressions, as well as sex differences in regions subserving social and self-evaluative processes. However, testosterone levels exhibited inverse patterns of association with neural response compared to pubertal stage in females (e.g. U-shaped relationship with the amygdala and hippocampus). Findings highlight potentially unique roles of age, pubertal stage and testosterone on socio-emotional development during adolescence, as well as sex differences in these associations.

neuroscience↗