Abstracts 313

Objective: To determinate the effects of low frequency rTMS (0.5 Hz) in

the EEG power spectrum in a sample of healthy subjects.

Method: Five healthy right-handed subjects (four men and one woman,

mean age 29.6 6 5.1 years) were studied. One session of 30 minutes of re-

petitive transcranial magnetic stimulation (rTMS) with 900 pulses, inten-

sity of 110% of motor resting thershold (MRT) and 0.5 Hz frequency

was carried out. The rTMS was made with an eight rounded coil over

the left motor cortex. A 19 leads EEG was recorded just before rTMS,

10 minutes after rTMS, 20 minutes after and finally after 30 minutes of

stimulation. We analyze the EEG power spectrum of all records, obtaining

the absolute power of each one of the frequency bands in each one of the

leads. Changes in power were evaluated statistically with a Wilcoxon Test.

The power spectrum in the C3 lead was compared with the contralateral

side (C4) in each one of the moments.

Result: In C3 the mean absolute power of the alpha band was of

12.79 6 5.11 mV2/Hz before rTMS, 10 minutes after rTMS the mean ab-

solute power was of 10.68 6 4.43 mV2/Hz , 20 minutes after rTMS the

mean absolute power was of 10.31 6 4.39 mV2/Hz and finally 30 minutes

after rTMS the mean absolute power was of 13.21 6 5.38 mV2/Hz. Only

significant differences in the alpha band were found after 20 minutes of

rTMS (p 5 0.043).

The mean absolute power of the beta band was of 1.56 6 0.38 mV2/Hz be-

fore rTMS, 10 minutes after rTMS the mean absolute power was of

1.48 6 0.39 mV2/Hz , 20 minutes after rTMS the mean absolute power

was of 1.45 6 0.53 mV2/Hz and finally 30 minutes after rTMS the mean

absolute power was of 1.36 6 0.26 mV2/Hz. Only significant differences

in the beta band were found after 10 minutes of rTMS (p 5 0.043).

In delta and theta bands no significant differences were found in this lead

(p . 0.05).

Conclusion: Low frequency rTMS over the left motor area gave rise to a

significant reduction of the absolute power 20 minutes after rTMS in the

alpha band and 10 minutes after rTMS in the beta band. Not changes were

observed in the contralateral motor area in these bands.

The authors are grateful to Hector Belmont for technical assistance.

tDCSPoster Only

231 Anodal transcranial direct stimulation enhances motor

dexterity and procedural memory consolidation

Assenza G1, Zappasodi F2, Tombini M1, Barbati G3, Tecchio F4,Rossini PM1, 1Campus Bio-Medico University (Rome, IT); 2Associazione

Fatebenefratelli per la ricerca, ISola Tiberina (Rome, IT); 3Department of

Public Health and Microbiology, University of Torino (Torino, IT);4Istituto di Scienze e Tecnologie per la Cognizione, CNR (Rome, IT)

Objective: Dynamic recruitment of primary motor cortex (M1) has been

identified during within-session and inter-session motor learning. Anodal

transcranial direct current stimulation (A-tDCS) has been demonstrated to

increase cortical excitability.

Our aim was to investigate M1 A-tDCS effect on within-session and

intersession motor learning.

Methods: Thirty right-handed healthy subjects (30 6 7 years) were asked

to repeat as higher number of a sequence (9 digits from 1 to 4) as possible

in 30sec-long blocks.

Sequences were displayed on a screen and subjects taped the correspond-

ing keys by the left fingers on a keyboard. In the pre-stimulation session, a

sequence (Sk) was learned, intermingled by random sequences (Sr), as

follows: Sr1-Sr2-Sk-Sk-Sk-Sk-Sk-Sr3-Sk-Sk-Sk-Sk-Sk-Sr4. Then a de-

clarative memory (paired-words recalling) task was performed.

Subjects randomly underwent 15min-long 1 mA A-tDCS or sham stim-

ulation. The 2 groups were comparable for sex, age, and use of musical

instruments. The anodal electrode (35 cm2) was positioned over the right

M1 (C4 of the 10-20 EEG International System), the reference electrode

(35 cm2) over the right shoulder.

In the post-stimulation session the following blocks were shown: Sr5-Sk-

Sk-Sk-Sk-Sk-Sr6- Sr6-Sr6-Sr6-Sr6. The declarative memory task was

again performed. For each block, the median time of right-executed

sequences was estimated as performance index. The ratio of wrong-

executed sequences was also evaluated.

Results: All subjects reached a performance plateau for Sk in the pre-

stimulation session. Anodal stimulation decreased execution time execu-

tion time in the first Sk of the post-stimulation session with respect to the

plateau (p , 0.0005), as opposed to sham-stimulated subject. The stimula-

tion effect was not present between random sequences (Sr4-Sr5). In the

post-stimulation session all subject showed a learning effect: sham-stimu-

lated early reached a plateau, while anodal-stimulated continued learning,

reaching higher performances (p , 0.001). No differences either in the per-

centage of wrong-executed sequences per block or in the declarative mem-

ory task performances were present between groups.

Conclusions: We demonstrated A-tDCS of M1, improving within-session

and inter-session motor learning, could improve both manual dexterity and

short-term procedural memory consolidation. A-tDCS effect was specific

for procedural memory, not affecting declarative memory.

rTMSPoster Only

232 rTMS over the right dorsolateral prefrontal cortex down-

modulates the computation of values in decision-making

Camus M, Halelamien N, Shimojo S, O’Doherty J, Camerer C, Rangel A,

California Institute of Technology (Pasadena, US)

Several studies have shown that activity in the orbitofrontal cortex (OFC)

and the right dorsolateral prefrontal cortex (rDLPFC) correlates with the

values assigned to items at the time of decision-making1,2. The role of the

rDLPFC in the valuation process is unknown. In particular, it is not known

whether the rDLPFC plays a causal role in decision-making, or if it

implements computations that are correlated with valuations, but that do

not participate in the valuation process itself. We addressed this question

by using repetitive transcranial magnetic stimuluation (rTMS) while

subjects were involved in an economic valuation task. Our results suggest

that rDLPFC plays a causal role in the computation of values: compared to

a control condition, applying rTMS to the rDLPFC causes a decrease in the

average values assigned to items as well as a decrease of the sensitivity of

the values to their underlying appetitive traits.

Acknowledgements: This study was supported by grants from the Gordon

and Betty Moore Foundation to AR and CFC and the Caltech Brain

Imaging Center.

References:1. Padoa-Schioppa, C and Assad, J.A (2006). Neurons in the orbitofrontal

activation is critical for preference judgments. Neuroreport 14, 1311-1315.

2. Plassman, H., O’Doherty, J. and Rangel, A (2007). Orbitofrontal cortex

encodes willingness to pay in everyday economic transaction. J Neurosci

27, 9984-9988.

TMSPoster Only

233 Effect of unilateral voluntary contraction of lower-limb muscles

on motor evoked responses in the contralateral resting leg

Perez MA1, Neilsen JB2, Cohen LG1, 1NIH (Bethesda, US); 2University of

Copenhagen (Copenhagen, DK)

A unilateral voluntary contraction of an upper limb muscle facilitates

motor evoked potentials (MEPs) in the contralateral agonist (Perez and

Cohen 2008) and antagonist muscle (Hortobagyi et al., 2003). It is

unknown whether this facilitation is also observed in the lower limb