Abstracts

There is no established paradigm for cortical stimulation for brain mapping, but the occurrence of unwanted afterdischarges (ADs) is an impediment to cortical mapping. Most epilepsy centers use 50Hz frequency and 0.2-0.3ms pulse width for this purpose. We compared the incidence of ADs using two sets of stimulation parameters i.e., different pulse frequencies (50 and 100Hz), and intensities (1 and 0.2ms width)., Subdural platinum grid electrodes of 2.3 mm diameter were implanted as part of presurgical evaluation in a 58 year old male with refractory left temporal lobe epilepsy. Direct cortical stimulations were performed extraoperatively using an Ojemann stimulator during multiple sessions on different days. AEDs were stable across the test days. Each pair of electrode was stimulated with the starting intensity of 1mA and pulse width of 1ms for 2 and 5s. The intensity was increased stepwise by 1mA up to 15mA until a clinical response or ADs appeared. Some of the electrode pairs were stimulated in a different session using the same method but with pulse width of 0.2ms. Statistical analysis was done using Chi-square test., Twenty-four pairs of electrodes were stimulated using either or both frequencies of 50 and 100Hz. Fifteen electrode pairs were stimulated using 1ms pulse width and 14 with 0.2ms while 5 pairs were tested using both paradigms. Among the electrode pairs that were stimulated with 0.2ms pulse width ADs occurred more often in 8/14 pairs that were stimulated with 100Hz for 5s (33% (44/131)), than 9/14 pairs that were stimulated with 50Hz for 5s (21% (24/111)) (p [lt] 0.05). Among the electrode pairs that were stimulated with 1ms pulse width AD occurrence was not significantly different between 12/15 pairs that were stimulated with 100Hz for 5s (77% (55/71)), and 11/15 pairs that were stimulated with 50Hz for 5s (61% (81/131))., This preliminary data showed lower risk of ADs with 50Hz compared to 100Hz during cortical stimulation using 0.2ms pulse width. Afterdischarges occurred more frequently and were equally common when the pulse width was increased to 1ms.,