Society for Neuroscience 2004, San Diego, CA (USA)
 
Orthography dependent high oscilatory activity in the basal temporal area
 
K. Tanji1(1), K. Suzuki(2), A. Delorme(3), H. Shamoto(4), N. Nakasato(4)
 

1. Graduate School of International Cultural Studies,

2. Department of Neuropsychology, Tohoku Univ, Sendai, Japan

3. Computational Neurobiology Lab, Salk Institute, La Jolla, CA, USA

4. Department of Neurosurgery, Kohnan Hospital, Sendai, Japan

kaztanji@pa2.so-net.ne.jp

 
    High frequency field potential activities have been shown to reflect various cognitive processes. Recently, high-gamma activity (HGBA) with frequencies up to above 100Hz has been observed in studies with invasive electrocorticogram (EcoG) in response to motor, perceptual and linguistic processes with discrete and specific spatial pattern. We recorded ECoG from subdural electrodes placed on bilateral basal temporal cortex in an epilepsy patient while he performed a lexical decision task on different forms of Japanese characters and a naming task. HGBA time-locked to stimulus presentations were observed in specific channels over a wide frequency range most prominently in about 60-140 Hz. In contrast to bilateral activation seen in a naming task, HGBA was left-lateralized in a lexical decision task. Significant dissociation in magnitude, but not in the location of HGBA was observed between two orthographic systems in Japanese, kanji and kana. Also, there were significantly larger GBA for kanji pseudowords compared to kanji words, most prominently in 80-120Hz. No detectable HGBA was induced by auditory word stimuli in this area. These results are in agreement with previous studies showing that the basal temporal area is important in conversion of orthography/semantics to phonology. The result suggests that high frequency oscillatory activity is a good correlate of higher visual cognitive functions.