EFFECTIVE SPREAD AND TIMECOURSE OF NEURAL INACTIVATION CAUSED BY LIDOCAINE INJECTION IN MONKEY CEREBRAL-CORTEX

We studied the effective spread of lidocaine to inactivate neural tiss ue in the frontal cortex of the rhesus monkey. Injections of 2% lidoca ine at 4 mu l/min were made while units were recorded 1 or 2 mm away. To inactivate units 1 mm away from the injection site 100% of the time , 7 mu l of lidocaine had to be injected. To inactivate units 2 mm awa y from the injection site 100% of the time, 30 mu l of lidocaine were required. Units were maximally inactivated around 8 min after the star t of a lidocaine injection, and they gradually recovered, regaining mo st of their initial activity by around 30 min after the start of an in jection. The volume of lidocaine required to inactivate neurons greate r than or equal to 90% of the time could be estimated by the spherical volume equation, V = 4/3 pi (r)(3). To prolong the inactivation, a sl ower infusion of lidocaine subsequent to an initial bolus was effectiv e. Saline control injections had no effect. These results allow both a prediction of the timecourse of neural inactivation and an estimate o f the spread of neural inactivation following injection of lidocaine i nto the monkey cerebral cortex. (C) 1997 Elsevier Science B.V.