, 2007, Kutner et al., 2004 and Law et al., 2005). We analyzed the monkey LFP data using the same multiple linear regression β weight analysis used on the human BOLD fMRI signals, examining nonoverlapping frequency bandwidths in the gamma (30–100 Hz) and beta (10–25 Hz) ranges derived from spectral analyses (Figures S1A and S1B available online). In some selleck chemicals cases where there was not enough data available to carry out a multiple regression analysis, we used standard parametric statistics to analyze the LFP data. The results of each analysis were compared across species to identify similarities as well as differences

in the neurophysiological responses. A common finding from the monkey entorhinal cortex has been strong responses to relatively novel stimuli (stimuli seen for the first time in the current session) compared to highly familiar stimuli (significant exposure over multiple days to months) (Brown et al., 1987, Suzuki et al., 1997 and Xiang and Brown, 1998). Few if any such signals have been reported in the hippocampus (Brown et al., 1987 and Xiang and Brown, 1998). We first asked whether

differences in responses to new versus highly familiar stimuli could be found in the monkey LFP signals. LFP sweeps were converted to frequency spectra and the mean log power from both the beta and selleck products gamma bandwidths of a 1,100 ms epoch spanning the scene and delay periods

were derived. The spectral power values from the selected bandwidths were then analyzed with multiple regressions for each session to generate β values for both the new and the highly familiar reference stimuli. These β values were then compared across sessions using parametric tests. For the monkey entorhinal cortex, significant differences between new and reference β values were found for the beta bandwidth (t(52) = 5.69; p < 0.0005), but not the gamma bandwidth (t(52) = 0.323; p = ns; Figure 2A). The direction of the effect in the beta bandwidth favored reference Metalloexopeptidase over new trial spectra. During separate recording sessions in the monkey hippocampus, significant differences in β values were found for both the beta (t(39) = 3.15; p < 0.003) and the gamma (t(39) = 2.35; p < 0.024) bandwidths. Additional analyses done to examine the detailed structure of signal showed that the differential signals we observed arose from a transient decrease during the scene/delay period relative to the fixation period that was larger (more negative) for the new conditions than for the reference conditions (Figures S1C–S1F). In humans, we applied a multiple regression analysis of the fMRI data calculating coefficients for the new and reference trial responses for each subject. The β values reflected the difference in activity between mnemonic and non-mnemonic tasks for each voxel.