Photic Driving
Posted on
October 20, 2023
Let's learn all the facts about a brain pattern called
Photic Driving
!
Photic Driving
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Learning EEG
Yamada, Thoru, and Elizabeth Meng. Practical Guide for Clinical Neurophysiologic Testing: EEG. Available from: Wolters Kluwer, (2nd Edition). Wolters Kluwer Health, 2017.
JCNP-D-16-00133 303..307 (acns.org)
The most commonly used sensory stimulation for provocation in EEG is photic stimulation. During this stimulation, a light is flashed repetitively in trains (10 to 30ms) of increasing frequencies using a stroboscope. The flash is repeated at 1 to 30 Hz with cycles of 10sec on 10sec off. The lamp is placed equally and directly in front of the patient’s eyes at about 30 cm away. This stimulation may be performed with the patients' eyes open or closed.
Photic driving is a response that occurs when the background rhythm (PDR) becomes time locked and in sync with each light flash. This is a normal response to have and just as normal not to have on an EEG. The photic driving response if present should be symmetrical, a lack of symmetry could suggest an underlying dysfunction of the occipital / posterior brain regions.
Photic stimulation is done primarily to elicit a photoparoxysmal response for the diagnosis of photosensitive epilepsy. PS provides other physiological responses but of less diagnostic value. A photoparoxysmal response (PPR)is defined by consistent emergence of discharges at a certain frequency of photic stimulation. PPR is one of the most well-known facets of epilepsy, but rare. It describes the emergence of interictal activity as a result of photic stimulation. Typically, this interictal activity is generalized or focal occipital, arises during but outlasts the photic stimulation itself, and is always reproducible at the same frequency of light flashes.