Working memory of somatosensory stimuli: An fMRI study Nicoletta Savini a, ⁎, Marcella Brunetti a, b , Claudio Babiloni c, d , Antonio Ferretti a, b a Department of Neuroscience and Imaging, University “G. d'Annunzio” of Chieti, Italy b ITAB — Institute for Advanced Biomedical Technologies, University “G. d'Annunzio” Foundation, Chieti, Italy c Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy d IRCCS San Raffaele Pisana, Roma, Italy abstract article info Article history: Received 27 April 2012 Received in revised form 16 August 2012 Accepted 14 September 2012 Available online xxxx Keywords: Working memory Tactile fMRI N-BACK task Fronto-parietal circuit In a previous study, we have shown that passive recognition of tactile geometrical shapes (i.e. no exploratory movement) engages prefrontal and premotor areas in addition to somatosensory regions (Savini et al., 2010). In the present study we tested the hypothesis that these regions are involved not only in the perception but also during working memory of such somatic information. We performed functional magnetic resonance imaging (fMRI) during the execution of N-BACK tasks, with 2D geometrical shapes blindly pressed on the subjects' right hand palm. Three conditions with increasing memory load (0-BACK, 1-BACK, 2-BACK) were used. Results showed that primary somatosensory area (SI), secondary so- matosensory area (SII) and bilateral Insula were active in all conditions, confirming their importance in coding somatosensory stimuli. Activation of fronto-parietal circuit in supplementary motor area (SMA), right superior parietal lobe (rSPL), bilateral middle frontal gyrus, left inferior frontal gyrus, and right superior frontal sulcus was significantly larger during 1-BACK and 2-BACK than 0-BACK. Left superior parietal lobe and right frontal eye field showed a higher activation during the 2-BACK than 0-BACK. Finally, SMA and rSPL were characterized by a statistically significant higher activation during 2-BACK than 1-BACK, revealing their sensitivity to the mem- ory load. These results suggest that working memory of tactile geometrical shapes (no exploratory movement) involves a complex circuit of modal and supramodal fronto-parietal areas. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Working memory (WM) is defined as the ability to transiently store and manipulate information held “on-line” to be used for cognition or for behavioral guidance (Baddeley, 1996, 2003). WM is typically modeled as a “central executive” attentive system supported by a second, more peripherally-based storage system, interacting together for information encoding and manipulation, in order to subserve planning, reasoning and problem solving (Baddeley, 1996, 2003; Goldman-Rakic, 1996). Neuropsychological studies have used several paradigms to disentan- gle different aspects of working memory in humans, such as continuous updating of information (i.e. on-line manipulation), maintenance of infor- mation, and information storage. One of the most used paradigms is the N-BACK task, which combines maintenance and encoding, as well as monitoring of a continuous sequence of stimuli (Fletcher and Henson, 2001). The majority of neuroimaging studies of human working mem- ory mainly employed visuo-spatial and verbal N-BACK tasks. A meta- analysis of 24 neuroimaging (positron emission tomography and functional magnetic resonance imaging, fMRI) studies using N-BACK tasks of verbal and visuospatial information has emphasized the role of a fronto-parietal network including lateral premotor cortex, dorsal cingulate and medial premotor cortex, dorsolateral and ventrolateral prefrontal cortex, frontal poles, medial and lateral posterior parietal cor- tex (Owen et al., 2005). Nevertheless, the cortical circuits underlying the working memory load elicited by N-BACK tasks using tactile inputs are still poorly under- stood. Several studies have used 1-BACK condition (i.e. subject has to maintain in WM the stimulus before the target) to investigate a sequential discrimination of haptically explored objects (Kaas et al., 2006) and visual and/or tactile stimuli (Stoeckel et al., 2003; Ricciardi et al., 2006). The re- sults showed that during visual and tactile spatial WM a supramodal fron- tal or fronto-parietal network was recruited in all sensory modalities. Noteworthy, the lack of studies performing a tactile 2-BACK task limits a detailed analysis of memory load effects on tactile input process- ing. In particular, it is not clear if the premotor and parietal networks sen- sitive to the verbal and visual memory load (Ragland et al., 2002; Carlson et al., 1998; Owen et al., 2005) are involved even in the manipulation and maintenance in memory of somatosensory information. In a previous study, we have shown that passive recognition of tactile geometrical shapes (i.e. no exploratory movement) engages prefrontal and premotor areas in addition to somatosensory regions (Savini et al., 2010). In the present study we tested the hypothesis that these regions are involved not only in the perception but also International Journal of Psychophysiology xxx (2012) xxx–xxx ⁎ Corresponding author at: Institute for Advanced Biomedical Technologies, University “G. D'Annunzio” of Chieti, Via dei Vestini, 33, 66013 Chieti (CH), Italy. Tel.: +39 0871 3556952; fax: +39 0871 3556930. E-mail address: nsavini@unich.it (N. Savini). INTPSY-10532; No of Pages 9 0167-8760/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijpsycho.2012.09.007 Contents lists available at SciVerse ScienceDirect International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho Please cite this article as: Savini, N., et al., Working memory of somatosensory stimuli: An fMRI study, International Journal of Psychophysiology (2012), http://dx.doi.org/10.1016/j.ijpsycho.2012.09.007