Understanding time perception through non-invasive brain stimulation techniques: A review of studies.

The present review includes transcranial magnetic and transcranial electric stimulation studies on time perception and shows that the neural processing of time requires the activity of wide range-distributed brain networks. Moreover, a critical discussion regarding non-invasive brain stimulation in the study of time processing is included to give the reader insights into the study of temporal processing in neuroscience. The cerebellum and auditory cortex seem most crucial when participants are required to estimate the passage of sub-seconds intervals and this conclusion holds independently of the modality used to mark the temporal intervals. Conversely, the primary visual area and MT/V5 seem to process primarily visual stimuli. The areas included in the prefrontal cortex are mostly implicated in the processing of supra-second time intervals and when time is processed in conjunction with other cognitive functions. Although previous fMRI studies showed activation in the supplementary motor area during sub-second timing tasks, TMS studies failed to confirm these observations. We conclude that the contribution of these strongly interconnected structures in the processing of temporal information is not fixed; their contribution depends not only on the duration of the time interval to be assessed by the brain but also on the cognitive set involved in the chosen task and on the stimulus modality used for marking time. Critical observations regarding the specificity of each method of stimulation as well as limitations and criticisms of the studies that used brain stimulation techniques will be also discussed.