Temporal Interactions between Maintenance of Cerebral Cortex Thickness and Physical Activity from an Individual Person Micro-Longitudinal Perspective and Implications for Precision Medicine

Abstract

Maintenance of brain structure is essential for neurocognitive health. Precision medicine has interests in understanding how maintenance of an individual person's brain, including cerebral cortical structure, interacts with lifestyle factors like physical activity. Cortical structure, including cortical thickness, has recognized relationships with physical activity, but concepts of these relationships come from group, not individual, focused findings. Whether or how group-focused concepts apply to an individual person is fundamental to precision medicine interests but remains unclear. This issue was studied in a healthy man using concurrent micro-longitudinal tracking of magnetic resonance imaging-defined cortical thickness and accelerometer-defined steps/day over six months. These data permitted detailed examination of temporal relationships between thickness maintenance and physical activity at an individual level. Regression analyses revealed graded significant and trend-level temporal interactions between preceding activity vs. subsequent thickness maintenance and between preceding thickness maintenance vs. subsequent activity. Interactions were bidirectional, delayed/prolonged over days/weeks, positive, bilateral, directionally asymmetric, and limited in strength. These novel individual-focused findings in some ways are predicted, but in other ways remain unaddressed or undetected, by group-focused work. We suggest that individual-focused concepts of temporal interactions between maintenance of cortical structure and activity can provide needed new insight for personalized tailoring of physical activity, cortical, and neurocognitive health.

Keywords: accelerometer; cortical thickness; human individuality; idiographic; intraindividual; physical activity; precision/personalized medicine; steps/day exercise.

Figure 1

Concurrent micro-longitudinal tracking of maintenance of right (A) and left (B) hemisphere mean cortical thicknesses and step-per-day activity (C). In (A,B) filled circles indicate scan A, and open circles indicate scan B; breaks in the lines indicate missing data at weeks 2, 6, and 7. Vertical dashed lines in (A–C) correspond to first and last scan days. Scatterplots of number of steps (D) and graphs of mean (±SD) steps (E) for each day of the week.

Figure 2

Scatterplots, linear regression lines, and associated R² for relationships between average steps/day during preceding weeks 1–3 (A) and 4–6 (B) vs. subsequent thickness maintenance. (C) R² profile summary for these preceding multi-week periods. The R² profile suggests associations were delayed/prolonged over weeks, with a temporal gradient involving a significant positive relationship for weeks 1–3 and no relationship for weeks 4–6.

Figure 3

Scatterplots, linear regression lines, and associated R² for relationships between average steps/day during preceding individual week 1 (A), 2 (B), and 3 (C) vs. subsequent thickness maintenance. (D) R² profile summary for preceding individual weeks 1–4.

Figure 4

Scatterplots, linear regression lines, and associated R² for relationships between average steps/day during preceding early week segments of weeks 1 (A), 2 (B), and 3 (C), and for preceding latter week segments of weeks 1 (D) and 2 (E) vs. subsequent thickness maintenance. (F) R² profile summary for week segments of preceding weeks 1, 2, and 3. The R² profile suggests a delayed/prolonged gradient in associations involving: first, early week segments that had a significant (s) positive relationship during preceding week 2 and trend (t)-level positive relationships during preceding weeks 1 and 3, and second, no relationships for latter week segments.

Figure 5

Scatterplots, linear regression lines, and associated R² for relationships between steps during indicated individual early week segment days (A–F) and latter week segment days (G,H) of preceding week 1 (top), 2 (middle), and 3 (lower) vs. subsequent thickness maintenance. (I) R² profile summary indicating significant (s) and trend (t)-level positive relationships for preceding individual days. R² at and below the dashed line are not significant. In (I), for each week Sunday is labeled and followed in sequence by Monday–Saturday.

Figure 6

Scatterplots, linear regression lines, and associated R² for relationships between steps during early week segment individual days of preceding weeks 1 (A), 2 (B,C), and 3 (D) and latter week segment individual days of preceding weeks 1 (E) and 2 (F) vs. subsequent thickness maintenances of separate right and left cortices. Identification of right and left cortices as indicated in (A) also applies to (B–F).

Figure 7

R² profile summaries for preceding thickness maintenance vs. average steps/day during subsequent 3-week periods (A), individual week periods (B), and early- and latter-week segments (C). Significant (s) and trend (t)-level associations are indicated; measures at and below the dashed lines were not significant. In (C), sequence of early (left bar) and latter (right bar) week segments indicated for week 1 also applies to each other week.

Figure 8

Scatterplots, linear regression lines, and associated R² of relationships between preceding thickness maintenances of separate left and right cortices vs. average steps/day during subsequent weeks 1–3 (A), 4–6 (B), and 7–9 (C). The convention distinguishing right and left cortices in (A) also applies to (B,C).