Modulation of slow brain potentials by working memory load in spatial and nonspatial auditory tasks Pia RaÈmaÈ a, *, Liisa Paavilainen a , Irina Anourova a , Kimmo Alho b, c , Kalevi Reinikainen b , Sampsa SipilaÈ a , SynnoÈve Carlson a, b a Institute of Biomedicine, Department of Physiology, University of Helsinki, PO Box 9, FIN-00014, Helsinki, Finland b Cognitive Brain Research Unit, Department of Psychology, University of Helsinki, Helsinki, Finland c Department of Psychology, University of Tampere, Tampere, Finland Received 23 June 1999; received in revised form 29 November 1999; accepted 22 December 1999 Abstract Slow event-related brain potentials were recorded from the human scalp during spatial and nonspatial auditory delayed matching-to-sample and n-back tasks to ®nd out whether there are dierences in the distribution of slow potentials during the retention of audiospatial and pitch information. The performance of both the location and pitch tasks produced slow potentials during the delay phase of the memory tasks. The delay-related slow potential was modulated by the amount of information to be processed during the tasks at the parietal±occipital sites. The distribution of mnemonic modulation was, however, not dierent between the tasks. The results suggest that there is integration of auditory information processing in the neuronal networks engaged in mnemonic processing of pitch and location. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Sound location; Pitch; Memory load; Slow event-related potentials; Human 1. Introduction Spatial and nonspatial information processing has been mainly studied in the visual system, and several lines of evidence suggest that there is segregation of visual information processing to the ventral `what' and dorsal `where' pathways [22,30]. It has been further suggested that this segregation is preserved also in the prefrontal cortical areas involved in visual working memory processing [7,20,26,33]. In these studies, acti- vation related to spatial and nonspatial working mem- ory has been directly contrasted, and the results indicate a dissociation of these memory functions. Although there are several studies in which auditory memory for tones [13], environmental sounds [5], melodies [36], and sound locations [2] has been investi- gated, spatial and nonspatial auditory processing has not been directly contrasted in any of them. The performance of a pitch comparison task has been shown to be disrupted by tones but not by audi- torily presented digits, indicating that mnemonic pro- cessing of pitch information is selectively disrupted by domain speci®c information [8]. Pitch discrimination has been shown to activate the right inferior frontal gyrus in contrast to the left prefrontal activation in phonetic discrimination [35]. In more recent behavioral studies, it has been shown that auditory memory for sound content and location was aected dierentially by selective interference, suggesting that neuronal pro- cessing of both spatial and nonspatial auditory infor- mation might be dissociated [1,6]. A lesion in the right Sylvian ®ssure and the inferior parietal lobe has been shown to induce inability to identify environmental sounds without de®cits in sound localization [28]. On the other hand, a lesion in the right temporal and insu- lar regions induced a de®cit in spatial and temporal Neuropsychologia 38 (2000) 913±922 0028-3932/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0028-3932(00)00019-1 www.elsevier.com/locate/neuropsychologia * Corresponding author. Tel.: +358-9-1911; fax: +358-9-191 8681. E-mail address: prama@cc.helsinki.® (P. RaÈmaÈ).