Event-related potentials as indirect measures of recognition memory

Event-related potentials (ERPs) were recorded during an auditory word-recognition task to determine whether they can be used as indirect measures of recognition memory, defined as the ability to differentiate learned from unlearned material when no overt recognition response from the subject is required. A modified version of the two-choice reaction time task developed by Allen, Iacono and Danielson (Allen et al., 1992) was used. In three recognition tasks, administered on two consecutive days, subjects were instructed to indicate recognition of recently learned words. These words were presented along with unlearned words and along with previously learned words which both required a non-recognition response. Recently learned target words as well as previously learned nontarget words elicited a centro-parietal positivity around 500-1000 ms post-stimulus. The size and onset of this late positivity (P300) were affected by the requirement of an overt recognition response. The results suggest that ERPs are sensitive to differences between learned and unlearned words, to some extent independently of the behavioral response. ERPs may therefore be used as indirect measures of recognition memory. In addition, because the present results held for stimuli presented in the auditory modality and because recognition indices were still observed after a one-day interval between learning and testing, this procedure might prove useful in various applications when the integrity of memory is in question

The bilateral origin of movement-related potentials preceding unilateral actions

It is as yet unclear why a unilateral self-paced movement in human and nonhuman primates is preceded by a bilateral Bereitschaftspotential (BP) or readiness potential (RP). The RP consists of an early symmetrical part (termed BP1 or RP), presumably of supplementary motor area (SMA) origin, and a later contralaterally dominant part (termed BP2 or NS'), to which the primary motor cortex (M1) is thought to contribute. Apart from the SMA there are other motor areas in the mesial cortex, which might provide additional sources for these slow waves. Although bilateral intracortical sources of the RP are found in the premotor cortex (Sasaki & Gemba, 1991), they play nearly any role in most discussions on the RP. Recently the very existence of the ipsilateral RP over MI has been doubted. RP recordings of two patients with an intracerebral electrode in the ventro-intermedius nucleus (Vim) of the thalamus are shown, suggesting that the ipsilateral RP is not the consequence of volume conduction or signal transmission via the corpus callosum. Rather they point to a subcortical source, from where the ipsilateral cortex is activated. Anatomical and recent RP recordings from Vim and subthalamic nucleus seem to support this interpretatio