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Vector-based phase classification of initial dips during word listening using near-infrared spectroscopy

Yoshino, Kayokoa,b; Kato, Toshinoria

doi: 10.1097/WNR.0b013e328359833b
COGNITIVE NEUROSCIENCE AND NEUROPSYCHOLOGY
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This study examined the classification of initial dips during passive listening to single words by analysis of vectors of deoxyHb and oxyHb measurements simultaneously derived from near-infrared spectroscopy. The initial dip response during a single-word 1.5-s task in 13 healthy participants was significant only in the language area, which includes the left posterior superior temporal gyrus and angular gyrus. Event-related vectors of responses to comprehended words moved significantly into phase 4, a dip phase, whereas vectors of responses to unknown words moved into a nondip phase (P<0.05). The same results were reproduced after previously unknown words were learnt by the participants. Among the five dip phases, reflecting variations in transient oxygen metabolic regulation during a task, the frequency of occurrence of hypoxic–ischemic initial dips (decreased oxyHb) was around three times that of the canonical dip (increased deoxyHb and oxyHb). Phase classification of event-related vectors enhances the slight amount of oxygen exchange that occurs in word recognition, which has been difficult to detect because of its small amplitude.

aDepartment of Brain Environmental Research, KATOBRAIN Co. Ltd, Tokyo

bKeio Research Institute at SFC, Kanagawa, Japan

Correspondence to Toshinori Kato, PhD, MD, 104-15-13 Shirokanedai 3, Minato-ku, 108-0071 Tokyo, Japan Tel/fax: +81 3 3440 0248; e-mail: kato@katobrain.com

Received July 5, 2012

Accepted August 19, 2012

© 2012 Lippincott Williams & Wilkins, Inc.