Neuropsychologia 48 (2010) 3069–3079 Contents lists available at ScienceDirect Neuropsychologia journal homepage: www.elsevier.com/locate/neuropsychologia The role of high-level visual areas in short- and longer-lasting forms of neural plasticity Andrea Pavan, Gianluca Campana ∗ , Marcello Maniglia, Clara Casco Department of General Psychology, University of Padua, Via Venezia 8, 35131 Padua, Italy article info Article history: Received 25 February 2010 Received in revised form 24 May 2010 Accepted 12 June 2010 Available online 18 June 2010 Keywords: Short-term synaptic depression Short-term synaptic facilitation Augmentation Rapid visual motion priming Rapid motion aftereffect Perceptual sensitization abstract Striate and extrastriate neurons present short-term synaptic depression and facilitation in response to brief stimulations. Recent psychophysical studies have shed light on some possible relationships between these short-term forms of neural plasticity and of psychophysical behavior. It has been shown that a brief adaptation to directional motion biases the perceived direction of a subsequently presented ambiguous test pattern towards the same direction to that of the adaptation (rapid visual motion priming – rVMP), but only after brief (40 ms) adaptation-test blank intervals. Although when the adaptation duration is increased, the perceived motion direction of the ambiguous test pattern is biased towards the opposite direction to that of the adaptation pattern (rapid motion aftereffect – rMAE). In the present study we stimulated MT and MST neurons via the presentation of contracting and expanding circular gratings. Our aim was to assess whether rapid effects exist at these higher levels of processing where neurons respond to optic flow, and if such effects are present determine their timescale. Results revealed strong rMAEs and perceptual sensitization (PS), which is a long-lasting facilitation that increases gradually when using intermediate and long adaptation-test blank intervals. We did not observe any effect of rVMP. Our results are considered to reflect the competition between coexistent forms of short- and long-term synaptic depression and facilitation implemented at different visual cortical circuitries. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Rapid forms of neural plasticity have been recently found in response to briefly presented visual stimuli (Chance, Nelson, & Abbott, 1998; Finlayson & Cynader, 1995; Lisberger & Movshon, 1999; Nelson, 1991; Priebe, Churchland, & Lisberger, 2002; Stratford, Tarczy-Hornuch, Martin, Bannister, & Jack, 1996). Authors of recent psychophysical studies on humans have proposed that such short-term forms of neural plasticity could provide the physiological substrate for rapid forms of motion aftereffect and visual motion priming (Kanai & Verstraten, 2005; Pavan, Campana, Guerreschi, Manassi, & Casco, 2009; Pinkus & Pantle, 1997). Short-term synaptic dynamics have been described in several cortical sites including the striate cortex and area MT of cats, rats and monkeys (Chance et al., 1998; Priebe et al., 2002; Varela et al., 1997; Varela, Song, Turrigiano, & Nelson, 1999). When two stimuli are presented in rapid succession, the neural response to the latter stimulus is considerably reduced, a phenomenon well known as short-term synaptic depression (Boudreau & Ferster, 2005; Chance et al., 1998; Finlayson & Cynader, 1995; Lisberger & Movshon, 1999; ∗ Corresponding author. Tel.: +39 049 8276651; fax: +39 049 8276600. E-mail address: gianluca.campana@unipd.it (G. Campana). Nelson, 1991; Priebe et al., 2002) or repetition suppression (RS, see Grill-Spector, Henson, & Martin, 2006 for a review). Priebe et al. (2002), for example, found that MT neurons respond to a motion step with a transient-sustained firing rate. The transition from an initial high firing rate to a lower sustained rate occurs over a tempo- ral window of 20–80 ms and can be considered a form of short-term adaptation. The authors found that the shift does not occur at the level of V1, but emerges from the intracortical circuit of area MT, and it is probably due to some forms of short-term synaptic depres- sion between MT neurons. However, other studies have found that brief stimulations are able to produce not only short-term depression but also short-term facilitation for subsequently presented stimuli, which leads to an increase of neuronal responsiveness (Castro-Alamancos & Connors, 1996; Hempel, Hartman, Wang, Turrigiano, & Nelson, 2000). Hempel et al. (2000) found, in both prefrontal and striate rats’ cortices, the presence of a strong short-term synaptic enhance- ment between interconnected units of the same region that could force a neuronal circuit to sustain persistent activity from sec- onds to minutes after a transient stimulus. The authors also revealed that short-term forms of depression and facilitation can coexist and compete; such synaptic dynamics are extremely important in managing the shaping of neural responses and their interactions. 0028-3932/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2010.06.018