1. Topographic mapping on memory test of verbal/spatial information assessed by event related potentials (ERPs) Petrini L¹², De Pascalis V², Arendt-Nielsen L¹, Chen ACN¹ ¹ Human Brain Mapping and Cortical Imaging Laboratory, Aalborg University (Denmark) ² Dipartimento di Psicologia, Università degli Studi di Roma "La Sapienza" (Italy) The present study was carried out for understanding how the human brain integrates diverse types of information into working memory. Although spatio-verbal integration has been investigated before by using PET/fMRI [1] and activities of single neurons [2], there are no ERP studies directly investigating this process. Temporal and topographic ERP responses obtained during tasks of verbal memory, spatial memory, and a combination of them were compared. Subjects were 15 healthy right-handed male students (age range 20 to 26, mean 23.4 years). A modified Sternberg recognition memory task, with three types of stimuli: 1) Digits; 2) Squares; 3) a Combination (squares and digits), was used. All the stimuli were presented one at a time in one of the nine equally spaced rectangles of a 3x3 grid. Three types of memory sets were created: 1) Digit, to decide whether or not the number matched any of the target items; 2) Location, to decide whether or not the square occupied the same spatial location; 3) Combined, to decide if digit and square were the same and occupied the same location. Each stimulus was presented for 500ms with an inter-stimulus interval of 1000ms. Next, a probe-recognition item appeared for 500ms. Subject’s response was determinated by pressing the mouse. The EEG was recorded from 128 scalp sites using the 10-5 system montage by ANT-EEProbe. Electrodes impedences were kept below 5KΩ. The EEG was digitezed at 512 Hz with amplifier bandpass of 0.3-30Hz. Repeated measures of ANOVAs (condition x hemisphere) were conducted. Post hoc comparisons of means were carried out by Tukey test (p<0.05). AIMS METHODS The data showed different amplitudes among the hemispheres on temporo-parietal and frontal areas between the memory tasks. The main findings are reported : 1. Negative activation around 170ms was lateralized on temporo- parietal areas of the right hemisphere compared with the left hemisphere (p<0.05). No significant difference was found among the memory tasks (Fig. 1) 2. Late negativity of the ERPs around 500ms was presented on the frontal regions of the left hemisphere. Difference among the hemispheres was found in digit and combined memory tasks (p<0.001) but not in location task (Fig.2). 3. Moreover, there is a tendency (not supported statistically) for digit and combined memory task to have a major negativity activation on right hemisphere than location task. In the present study, the temporal and topographic ERPs responses were investigated evaluating the early and late stages of processing by using ERPs when digit, location, and combination of them need to be recognized. The results showed an enhancement of temporo-parietal N170 on the right hemisphere in all memory tasks suggesting that this ERP component may be elicited not just by faces but also by other types of stimuli and may operate an early configurational analysis on few but salient elements. A subsequent negative shift found on the left-frontal area (N500) during digit but not during location was interpreted as dissociation between digit task vs. spatial task supporting previous literature results. Moreover, the results showed similar ERP patterns between digit and combined memory tasks. The data support that the left hemisphere is involved in rehearsal/retention operation for verbal as well as for integration of verbal and spatial information. RESULTS CONCLUSION Supported by Marie Curie Fellowship and Danish Technology Research Council ACKNOWLEDGEMENTS REFERENCES Fig. 1 Fig. 2 [1] Prabhakaran, V., Narayanan, K., Zhao, Z., and Gabrieli, J.D.E. (2000). Integration of diverse information in working memory within the frontal lobe. Nat. Neurosci. 3, pp.85-90. [2] Rao, S.C., Raimer, G., Miller, E.K. (1997). Integration of what and where in the primate prefrontal cortex. Science 276, 821-824.