‘What’ and ‘Where’ we remember: an anatomo-functional dissociation within Verbal Short-Term Memory

Recently, the anatomo-functional specialization of the cerebral areas involved in verbal Short-Term Memory network has been investigated on neurosurgical patients, highlighting how the two main areas of this network, the left Inferior Frontal Gyrus (IFG) and the left Supra-Marginal Gyrus (SMG), can be specialized in the storage of content information and of order information, respectively. In the present experiment, we aimed at replicating this evidence in healthy subjects through the use of repetitive Transcranial Magnetic Stimulation (rTMS). Twenty healthy subjects took part in a within-subjects experiment including three randomized sessions. In two sessions, offline 1 Hz rTMS was applied over either the left IFG or left SMG, while the third was a behavioural-only session. The experimental task was a computerized auditory-verbal digit span. Digit span showed a significant worsening of the accuracy after 1 Hz rTMS applied over both the left IFG and SMG. Furthermore, a reversed distribution of error type was observed: inhibiting IFG significantly increased the content/item errors, while inhibiting SMG increased order errors. We suggest that the SMG is specialized in storing order information, probably independently from the material type.