Conference proceeding
Hemodynamic response estimation during cognitive activity using fNIR spectroscopy
Foundations of Augmented Cognition, Vol 11, pp.207-209
01 Jan 2005
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Abstract
Near infrared spectroscopy (NIRs) enables measurement of the hemodynamic changes during funtional brain activation. Using the modified Beer-Lambert law and measurements performed at two different wavelengths within the near infrared light range (between 700-900nm) and different times, the relative changes in concentrations of deoxy-Hb and oxy-Hb can be obtained. These measurements led to the assessment of several types of brain functions such as, motor and visual activation, auditory stimulation and performance of cognitive tasks [1-3].
Modeling the hemodynamic changes is important for several reasons for example these models may lead to better statistical maps, or to the possibility of performing simulations with the model or more importantly they can allow the possibility to give a physiological interpretation of the model parameters.
There have been several studies in modeling the hemodynamic response in fMRI using FIR filters, statistical methods such as Bayesian modeling, or mathematical model fitting to Gaussian, Poisson or gamma type functions [4-9]. In this work, we implemented the latest approach in functional near infrared (fNIR) spectroscopy (fNIRs) and assume that each evoked hemodynamic response can be modeled by a gamma type function as given in the fugure 1. Once the evoked hemodynamic responses are estimated, features such as the maximum amplitude or the peak value of oxygenation activation and time to peak or response time can be extracted from the model which can further be used to quantify cognitive state of the subjects.
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There have been on-going studies in problem solving of graded difficulties (anagram solution). These studies, using both block and event-related anagram protocols, revealed that a wearable NIRs measurement of metabolic activation and blood flow can be valuable in educational aid [10]. In the event related anagram study subjects are presented an anagram for 1 sec. and given 15 sec. to solve it until the next presentation. This procedure allows the hemodynamic response to fully evolve which has been shown in the literature to take 10-12sec. period [8-9]. Event related (ER) studies provided insights as how to model the hemodynamic response and used widely in the assessment of cognitive activation in different regions of the brain for different task loads. However, in such studies, the protocol time is long and they do not reflect real world situations. In block anagram study, subjects are shown as many anagrams as they can solve within 1 min periods. Whenever subjects solved the anagram they press a certain button which results in immediate presentation of the next anagram. Since most of time subjects solve tha anagram within 2-5 sec. period, the hemodynamic responses overlap in time which present challenges to data analysis. Until now, in block anagram studies, it was not possible to evaluate the subject's responses in times or brain activation for single anagram presentation within a block for graded difficulty analysis.
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Details
- Title
- Hemodynamic response estimation during cognitive activity using fNIR spectroscopy
- Creators
- M IzzetogluS NiokaS BunceK IzzetogluB OnaralB Chance
- Contributors
- D D Schmorrow (Editor)
- Publication Details
- Foundations of Augmented Cognition, Vol 11, pp.207-209
- Publisher
- Taylor & Francis
- Number of pages
- 3
- Resource Type
- Conference proceeding
- Language
- English
- Academic Unit
- School of Biomedical Engineering, Science, and Health Systems
- Identifiers
- 991019170125504721
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- Computer Science, Cybernetics
- Ergonomics
- Psychology, Experimental