Investigating the brain energy dynamics during language activity

Abstract

The present dissertation aimed to measure the overall cognitive cost of language and visual processing to the brain with ear temperature measurement. Three verbal auditory experiments revealed that processing words caused a greater temperature in crease in the left ear than the right ear, indicating an expected left-hemispheric activity for language processing. Furthermore, processing words from a non-native language (English) caused greater cognitive cost (greater temperature increase) compared to words from the native language (Turkish). Lastly, it was found that the greatest tem perature increase was caused by the most difficult task. The last auditory experiment assessed the frontal cortex hemodynamics with functional near-infrared spectroscopy (fNIRS) and showed that the left hemisphere was active throughout the experiment, while the most difficult task caused the most widespread neuronal activity. A visual discrimination task revealed a greater temperature increase in the right ear compared to the left ear. These findings suggested that ear temperature can capture the overall cognitive cost of lateralized brain functions and can dissociate the task difficulty. A novel mental rotation (MR) and Turkish relative clause (RC) processing experiments were carried out with fNIRS to further investigate the cognitive cost of visual and lan guage processing as well as to assess the hemisphere’s contributions to processing. The MR experiment revealed a core neuronal activity in the right hemisphere regardless of the task difficulty and increased left-hemispheric activity with increased task difficulty. RC processing in Turkish was investigated with a neuroimaging method for the first time and it was shown that processing object RCs causes greater cognitive load than subject RCs, reflected by more widespread neuronal activity in the prefrontal cortex and greater non-significant hemodynamic activity in Broca’s Area.|Keywords: Tympanic Membrane Temperature, fNIRS, Language Processing, Visual Processing, Cognitive Cost.