Asymmetry of neuronal activity during extracellular microelectrode recording from left and right human temporal lobe neocortex during rhyming and line-matching

Recordings of neuronal activity in humans have identified few correlates of the known hemispheric asymmetries of functional lateralization. Here, we e xamine single-unit activity recorded from both hemispheres during two delay ed match-to-sample tasks that show strong hemispheric lateralization based on lesion effects; a line-matching (LM) task related to the right hemispher e, and a rhyming (RHY) task related to the left. Nineteen neuronal populati ons were recorded with extracellular microelectrodes from the left temporal neocortex of 11 awake patients, and 18 from the right in 9 patients during anterior temporal lobectomy for complex partial seizures under local anest hesia. All subjects were left hemisphere dominant for language. Twelve (32% ) populations exhibited statistically significant changes in activity p < . 05. Although changes in firing frequency were recorded from both hemisphere s during both tasks, the RHY task elicited changes in activity several hund red milliseconds earlier on the left side than on the right. The LM task, o n the other hand, induced changes earlier on the right side than on the lef t. Both hemispheres contained units active during verbal responses regardle ss of which behavior elicited the response. Our results indicate char cereb ral dominance is reflected in earlier neuronal activity in the anterior tem poral lobe during tasks lateralized to that hemisphere.