CEREBRAL LATERALIZATION OF NEURONAL-ACTIVITY DURING NAMING, READING AND LINE-MATCHING

Changes in human right or left temporal cortical neuronal activity dur ing language and visuospatial tasks were investigated during craniotom y under local anesthesia for medically intractable epilepsy in patient s known to be left dominant for language based on preoperative intraca rotid amobarbital perfusion testing. Extracellular recordings were obt ained from 57 neuronal populations (26 from the left hemisphere) in th e superior and middle temporal gyri of 34 patients. Frequency of activ ity was compared during overt and silent object naming, word reading a nd line-matching. Although all recordings were from the cortex not ess ential for language, statistically significant changes in activity dur ing these tasks were identified in 49% of the populations. Most popula tions showed significant changes to only one of the tasks, indicating discrete neural networks for reading and naming. Nearby neuronal popul ations recorded by the same microelectrode usually had different behav ioral correlates. There were no significant differences in the proport ion of neurons changing activity with language or spatial measures bet ween right (non-dominant) or left (dominant) temporal lobes. Left supe rior and middle temporal gyrus populations, however, demonstrated sign ificant early reductions in activity during overt or silent naming, wh ile right middle temporal gyrus recordings showed significant early in creased activity only during overt naming. Although reading measures e licited more activity from the non-dominant temporal lobe, early reduc tions in activity were recorded exclusively from the dominant side. Vi suospatial tasks evoked changes in neuronal frequency predominantly in the middle temporal gyrus, and during one of these tasks, significant later increases in activity were present bilaterally. Our results ind icate that the functional lateralization of cognitive behaviors may de pend less on the anatomic location of the associated neuronal activity than on the neurophysiologic characteristics of that activity.