Unilateral and bilateral cortical spreading depression interferes with radial maze performance in rats

Seven rats with implanted cortical electrodes were trained in a 12-arm radial maze to asymptomatic performance (1.38 errors per trial). Single waves of cortical spreading depression (CSD) were elicited by application of cathodal current to the parieto-occipital cortex and monitored by suppression of callosal responses in the frontal cortex. Bilateral CSD elicited before the trial caused a small increase of error incidence in choices 1-6 but did not affect accuracy of choices 7-12. Bilateral CSD between choices 6 and 7 increased error incidence in the second half of the trial from 1.33 to 2.84, i.e. almost to the chance level of 3.0. Unilateral CSDs elicited before the first half of the trial in one hemisphere and in the same or in the contralateral hemisphere before the second half of the trial caused similar deterioration of performance in choices 7-12 (2.4 and 2.1 errors, respectively). It is concluded that the CSD effects have both proactive and retroactive components and that the working memory record is not lateralized at the cortical level.