Low Intensity TMS Enhances Perception of Visual Stimuli.
Arman Abrahamyan, Colin W G Clifford, Ehsan Arabzadeh, Justin A Harris
Brain Stimulation June 27, 2015 DOI: 10.1016/j.brs.2015.06.012 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Experimental study Peer reviewed |
|---|---|
| Population | Human participants performing a visual orientation discrimination task |
| Intervention | Transcranial magnetic stimulation (TMS) |
| Measures | contrast thresholds |
| Keywords | Brain Visual cortex Humans Photic stimulation Visual perception Female Transcranial magnetic stimulation Young adult Discrimination, psychological Consciousness Orientation discrimination Contrast detection Pedestal effect |
| Key findings | Weak TMS over visual cortex improved contrast sensitivity for identifying gratings tilted 45 degrees from vertical, indicating that TMS sums with the visual signal while preserving orientation information. The authors propose a non-linear transduction mechanism and suggest low-intensity TMS can be used to push unconscious stimuli into consciousness. |
Abstract
Background: Transcranial magnetic stimulation (TMS) is a popular functional mapping tool in cognitive and sensory neuroscience. While strong TMS typically degrades performance, two recent studies have demonstrated that weak TMS, delivered to visual cortex, can improve performance on simple visual tasks. The improvement was interpreted as the summation of visually-evoked and TMS-elicited neuronal activity in visual cortex, but the nature of this interaction remains unclear.
Objective: The present experiments sought to determine whether these weak pulses of TMS assist subjects to see the visual stimulus itself or create a distinct "melded" percept that may not be recognizable as the visual stimulus.
Methods: We measured contrast thresholds in an orientation discrimination task in which participants reported the orientation (left or right) of gratings tilted 45° from vertical.
Results: Weak TMS improved sensitivity for identifying gratings, suggesting that TMS sums with but preserves orientation information so that the subject can recognize the visual stimulus. We explain the effect using a mechanism of non-linear transduction of sensory signals in the brain.
Conclusions: The capability of low-intensity TMS to augment the neural signal while preserving information encoded in the stimulus can be employed as a novel approach to study the neural correlates of consciousness by selectively "pushing" an unconscious stimulus into consciousness.