LTP‐like changes induced by paired associative stimulation of the primary somatosensory cortex in humans: source analysis and associated changes in behaviour

Abstract

Paired associative stimulation (PAS), which combines repetitive peripheral nerve stimulation with transcranial magnetic stimulation (TMS), may induce neuroplastic changes in somatosensory cortex (S1), possibly by long-term potentiation-like mechanisms. We used multichannel median nerve somatosensory evoked potential (MN-SSEP) recordings and two-point tactile discrimination testing to examine the location and behavioural significance of these changes. When TMS was applied to S1 near-synchronously to an afferent signal containing mechanoreceptive information, MN-SSEP changes (significant at 21-31 ms) could be explained by a change in a tangential source located in Brodmann area 3b, with their timing and polarity suggesting modification of upper cortical layers. PAS-induced MN-SSEP changes between 28 and 32 ms were linearly correlated with changes in tactile discrimination. Conversely, when the near-synchronous afferent signal contained predominantly proprioceptive information, PAS-induced MN-SSEP changes (20-29 ms) were shifted medially, and tactile performance remained stable. With near-synchronous mechanoreceptive stimulation subtle differences in the timing of the two interacting signals tended to influence the direction of tactile performance changes. PAS performed with TMS delivered asynchronously to the afferent pulse did not change MN-SSEPs. Hebbian interaction of mechanoreceptive afferent signals with TMS-evoked activity may modify synaptic efficacy in superficial cortical layers of Brodmann area 3b and is associated with timing-dependent and qualitatively congruent behavioural changes.

Contrasting functional imaging parametric maps: The mislocation problem and alternative solutions

“…In ECD modeling, an algorithm seeks the ECD (coordinates, orientation and amplitude) that best explains the field topography (or a restriction of it) at a given time (H€ am€ al€ ainen et al, 1993). Coordinates of ECDs in two different conditions can then be compared directly with a multivariate location test such as Hotelling T 2 test (Hotelling, 1931) or with other previously proposed methods (Litvak et al, 2007;Singh and Harding, 1996). Such procedure, however, requires that an ECD can actually be fitted in every subject, which is not always the case in real data.…”

Homeostatic Metaplasticity in the Human Somatosensory Cortex

“…Noninvasive stimulation techniques, such as repetitive transcranial magnetic stimulation (rTMS), paired associative stimulation (PAS), transcranial direct current stimulation, peripheral nerve stimulation or peripheral tactile stimulation, allow to study mechanisms of cortical plasticity in humans (Ziemann, 2004;Classen & Ziemann, 2003;Paulus, 2003;Pleger et al, 2001). For example, PAS can induce long-lasting bidirectional changes in excitability in the human primary motor cortex and in the somatosensory cortex depending on the interval between a pair of associative stimuli (Litvak et al, 2007;Müller, Orekhov, Liu, & Ziemann, 2007;Wolters et al, 2003Wolters et al, , 2005Ziemann, Ilic, Pauli, Meintzschel, & Ruge, 2004;Stefan, Kunesch, Cohen, Benecke, & Classen, 2000). These aftereffects are referred to as long-term potentiation (LTP)-like and long-term depression (LTD)-like plasticity as they resemble spike-timing dependent LTP and LTD of neuronal synapses (Cooke & Bliss, 2006).…”

A method to induce human cortical long-term potentiation by acoustic stimulation

“…The non-invasive recording methods such as EEG (electroencephalography) and MEG (magnetoencephalography) were employed to record the sensory-evoked responses [13]. Along this direction, there has been a significant amount of evidence on LTPs evoked by the sensory stimulation of touch [14], vision [15] and hearing [16]. The human LTP is found to be frequency-dependent, input specific, long-lasting (!1 hour), and limited by NMDA receptor blockers, which are similar to LTP found in animal experiments where LTP in the sensory neocortices has been fully established [11].…”