Hippocampus size predicts fluid intelligence in musically trained people

Abstract

Introduction Neurogenesis persists in the human adult hippocampus1 and the survival of new progenitor cells is enhanced by learning activities2. Using the musician's brain as a model for cortical plasticity, musical training induced functional adaptations of the hippocampus have been demonstrated3,4. Furthermore, there is evidence for a positive correlation between hippocampus size and fluid intelligence5, encompassing aspects of attention, working memory and executive functions6. Previous data strongly suggest that musical training impacts on such higher order cognitive functions7,14. Following these findings we hypothesize a linkage between hippocampus size and fluid intelligence in musically trained people. Methods Participants: Three groups - piano experts (E, n=20), piano amateurs (A, n=20) and nonmusicians (N, n=19), matched by age and gender. Task: short version of the Raven's Test, Advanced Progressive Matrices (time limit 15 minutes). Structural MRI: manual segmentation8,9,10,11,12 of left (LH) and right (RH) hippocampi done by a single investigator blinded for group belonging and ID of each subject, software MRIcroN13 (Fig. 1) Statistics: one-way ANOVAs on Raven performance and hippocampus volume; Fisher's r to z transformations; robust multiple regression models for each hemisphere: (i) to predict Raven performance by hippocampus volume and (ii) to test whether this prediction is modulated by the factor of musical training. Robust regression analysis (implemented by statistical software R) represents a valid alternative to least square regression analysis when data is potentially contaminated by single influential observations. Results One way ANOVAs with three levels of expertise: no main effects of Expertise neither in Raven's Test performance nor in hippocampus volumes. No main effect of Lateralization (Fig. 2). Pooling of musicians (M=A+E) justified as no difference in predictive power exists between A and E, neither in the left nor in the right hemisphere. LH: z=0.84, p=0.401, RH: z=-0.45, p=0.623. Robust multiple regression analysis testing the prediction of Raven's performance by hippocampus size, modulated by musicianship (two levels: N, M(A+E)): - Left hemisphere: Significant interaction (t=2.221, p=.030), revealing that prediction of Raven's performance by hippocampus size is modulated by musical training: N (beta =.03) and M (beta =.46). - Right hemisphere: Significant interaction (t=2.003, p=.050), revealing that prediction of Raven's performance by hippocampus size is modulated by musical training: N (beta =.01) and M (beta =.38). Conclusion Hippocampus size significantly predicts fluid intelligence performance in musically experienced subjects but not in musically naïve ones. This result represents a striking additional corroboration of musicians' brain plasticity. It seems highly plausible that a longlasting complex activity like musical instrumental training from childhood into adulthood induced an increase in hippocampus size associated with enhanced logical reasoning. Further research is needed to investigate cognitive functions favored by musical training and possible consequent impact on the development of peculiar brain structures. NB: This research was performed within the framework of an ongoing research project performed by Clara James (principal investigator) and postdoc collaborator Mathias Oechslin entitled "Behavioral, neuro-functional and neuro-anatomical correlates of experience dependant music perception" (FNS 100014_125050). This research project investigates brain adaptations in correlation with changes of behavior in young adults with varying musical experience, anticipating gradual changes in behavior, brain functioning and brain structure with degree of musical aptitude. In this frame, I did the data collection of hippocampus volumes and analyzed the results in correlation with a literature research on the subject