Prefrontal cortex connectivity during right and left hand dexterity tests in younger and older adults.

Test completion times were longer for Older adults than Younger adults for both the right and left hand 9-hole peg tests.

• Younger adults: 29 ± 4 years (10F:10M, n=20); Older adults: 67 ± 12 years (10F:9M, n=19)
• R9HPT and L9HPT completion times were longer for Older than Younger adults (p ≤ 0.001)
• Both groups took longer to complete the L9HPT than the R9HPT (p ≤ 0.001)
• All participants were healthy right-handed adults

Greater change in oxygenated hemoglobin (ΔO2Hb) was associated with longer test completion times in Older adults across multiple PFC regions.

• Greater ΔO2Hb was associated with longer test completion times in 5 of 8 PFC regions in Older adults
• ΔO2Hb was measured as the change in oxygenated hemoglobin from baseline to test completion using fNIRS
• fNIRS was positioned over eight PFC regions
• This association was not equivalently observed in Younger adults

Patterns of functional connectivity between PFC regions differed between R9HPT and L9HPT within each group and between age groups.

• Both Younger and Older groups showed connectivity between the right lower dorsolateral and left upper medial regions during the L9HPT
• The left upper medial, right upper medial, left lower medial, and left dorsal lateral regions were mostly involved with other PFC regions
• Connectivity patterns differed both within group (R9HPT vs. L9HPT) and between groups (Younger vs. Older)
• Time series analysis of ΔO2Hb was used to evaluate connectivity between pairs of PFC regions

Interhemispheric PFC connectivity was demonstrated during both R9HPT and L9HPT for both age groups.

• Both Younger and Older adults showed interhemispheric PFC connectivity during R9HPT and L9HPT
• Significant intrahemispheric PFC connectivity was shown for both R9HPT and L9HPT in the Older group
• In the Younger group, significant intrahemispheric PFC connectivity was shown only during L9HPT, not R9HPT
• These findings suggest age-related differences in the organization of PFC connectivity during motor tasks

Greater PFC connectivity associated with older age and non-dominant hand use did not result in improved task efficiency.

• Age and use of the non-dominant hand required more PFC connectivity
• Despite increased connectivity, this did not lead to improved task efficiency (i.e., shorter completion times)
• ΔO2Hb showed more pairing between regions during hand dexterity tasks performed by the non-dominant hand
• This finding applied across both age groups

fNIRS was used as a surrogate measure of neural activity over eight PFC regions during hand dexterity tasks.

• Functional near infrared spectroscopy (fNIRS) was positioned over eight PFC regions
• Neural activity was measured as ΔO2Hb (change in oxygenated hemoglobin) from baseline to test completion
• The 9-hole peg test (9HPT) was used as the hand dexterity task for both dominant (right) and non-dominant (left) hands
• The study included 20 Younger (29 ± 4 years) and 19 Older (67 ± 12 years) healthy right-handed adults