Temporal dynamics of memory trace formation in the human prefrontal cortex.
Event-related repetitive transcranial magnetic stimulation (rTMS) can dynamically interfere with the memory encoding of complex visual scenes. Here, we investigated the critical time elapsing from stimulus presentation to the formation of an effective memory trace by delivering rTMS (900 ms at 20 Hz) during the encoding of visual scenes at different poststimulus delays (from 100 to 500 ms) in 28 healthy volunteers. The stimulation delay showed a robust inverse correlation with the correct retrieval of encoded images. In particular, rTMS stimulation delivered with a delay of 500 ms and lasting for 400 ms after stimulus offset resulted in a huge drop in retrieval accuracy. Such a timing suggests that rTMS affects the formation of long-term memory through interference with postperceptual executive processes, rather than with perceptual analysis of the stimuli. The effect was specific for stimulation of the left dorsolateral prefrontal cortex (DLPFC), whereas rTMS applied to the right DLPFC, vertex (active control site), as well as sham stimulation (placebo) did not affect accuracy. These results confirm the crucial role of the left DLPFC in encoding and provide novel information about the critical timing of its engagement in the formation, consolidation, and maintenance of the memory trace.
Sezione Neurologia, Dipartimento di Neuroscienze, Universita` di Siena, I-53100 Siena, Italy. Rossisimo@unisi.it
Simone
S
Rossi
Iglis
I
Innocenti
Nicola R
NR
Polizzotto
Matteo
M
Feurra
Alberto
A
De Capua
Monica
M
Ulivelli
Sabina
S
Bartalini
Stefano F
SF
Cappa
D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D001931:Brain Mapping; D003463:Cues; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D009483:Neuropsychological Tests; D017711:Nonlinear Dynamics; D010775:Photic Stimulation / Q000379:methods; D017397:Prefrontal Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult