Sensory discrimination deficits in CTS. (A) Discrimination accuracy (percentage of correct trials) for median nerve innervated digits (D2 and D3) was significantly lower in CTS compared to healthy control subjects (HC) (CTS: 90.4 ± 12.4%, healthy control subjects: 98.4 ± 4.2%, mean ± SD P < 0.001, Mann-Whitney U-test). Accuracy for D5 did not differ between groups (CTS: 98.2 ± 8.2%, healthy control subjects: 100.0 ± 0.0%, mean ± SD Mann-Whitney U-test). (B) For subjects with CTS who did make errors, D2 and D3 accuracy was positively correlated with D2/D3 separation distance in contralateral S1 of the brain (r = 0.50 P < 0.05). Thus, closer D2/D3 separation distance was associated with reduced accuracy in discriminating median nerve innervated digits (D2 and D3) in four-finger forced choice sensory discrimination testing.