The purpose of this study was to determine the mediating neuroanatomy
of implicit and explicit sequence learning using a modified version of
the serial reaction time (SRT) paradigm. Subjects were seven healthy,
right-handed adults (three male, four female, mean age 26.7, range 18
-43 yr). PET data were acquired via the oxygen-15-labeled-carbon dioxi
de inhalation method while subjects performed the SRT. Subjects were s
canned during two blocks each of 1) no sequence (Random), 2) single-bl
ind, 12-item sequence (Implicit), and 3) unblinded, same sequence (Exp
licit). Whole-brain-normalized images reflecting relative regional cer
ebral blood flow (rCBF) were transformed to Talairach space, and stati
stical parametric maps (SPMs) of z-scores were generated for compariso
ns of interest. The threshold for significant activation was defined a
s z-score greater than or equal to 3.00. Behavioral data demonstrated
significant learning (P <.05) for Implicit and Explicit conditions. Te
sts of explicit knowledge reflected non-significant explicit contamina
tion during the Implicit condition. Foci of significant activation in
the Implicit condition were found in right ventral premotor cortex, ri
ght ventral caudate/nucleus accumbens, right thalamus, and bilateral a
rea 19; activation in the Explicit condition included primary visual c
ortex, peri-sylvian cortex, and cerebellar vermis. Activations in visu
al and language areas during the Explicit condition may reflect consci
ous learning strategies including covert verbal rehearsal and visual i
magery. Right-sided premotor, striatal, and thalamic activations suppo
rt the notion that implicit sequence learning is mediated by cortico-s
triatal pathways, preferentially within the right hemisphere. (C) 1996
Wiley-Liss, Inc.