The causal involvement of the right supramarginal gyrus in the subjective experience of time: A hf-tRNS study

Neural populations in the supramarginal gyrus (SMG) of the right hemisphere have been shown to be involved in processing the subjective experience of time, particularly because of their selectivity to specific temporal durations. To directly investigate this relationship, we applied high-frequency transcranial Random Noise Stimulation (hf-tRNS) on the right SMG during a duration judgment task: 24 participants were required to judge the duration of a test visual stimulus (350, 450, 550, 650 ms) as shorter or longer than the duration of a reference auditory stimulus (500 ms). In half of the trials this procedure was preceded by a visual adaptation paradigm, used as a tool to manipulate the subjective experience of time: for 12 participants the adaptor was shorter than the test (250 ms), and for 12 participants it was longer than the test (750 ms). All participants performed an online hf-tRNS session and a sham control session. For each participant and for each condition, the Point of Subjective Equality (PSE) was calculated and results revealed an expected negative aftereffect in the group exposed to a longer adaptor. Moreover, hf-tRNS modulated participants’ performance with respect to sham, confirming the involvement of the right SMG in temporal experience. Importantly, only in the group exposed to the longer adaptor, PSE values were higher during stimulation than during sham, only after the adaptation procedure (no difference emerged in trials without adaptation). This pattern of results confirms recent neuroimaging findings, and adds a direct evidence of the causal role of this area in subjective time experience.