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Nonlinear effects in the bold response for short stimulus duration heterogeneity of hemodynamic response

I. MENDICHOVSZKY1,* , A. FERRETTI2,3, C. DEL GRATTA2,3, M. CAULO3, C. COSMA1, G. L. ROMANI2,3

Affiliation

  1. Faculty of Environmental Science, “Babes-Bolyai” University, Cluj-Napoca, Romania
  2. Istituto di Tecnologie Avanzate Biomediche-Fondazione Università G. D'Annunzio, Chieti, Italy
  3. Dipartmento di Scienze Cliniche e Bioimmagini, Università G. D'Annunzio, Chieti, Italy

Abstract

Functional magnetic resonance imaging using the BOLD effect is a well established technique to investigate non-invasively brain function. Most functional magnetic resonance imaging studies use linear models to predict the observed BOLD response by convolving the stimulus profile with a haemodynamic response function. For very short stimulus durations (<2s) deviations from the linear model have been found in response area and amplitude. In this study we investigated the nonlinearities in the BOLD response in the human primary visual cortex for four very short stimulus durations (200, 400, 800 and 1000ms) and for a half visual field stimulation paradigm. The nonlinear behaviour of the BOLD signal was observed for all stimulus durations and was more pronounced for the shortest stimulus duration (200ms) both in response area and amplitude. No correlation in the BOLD response was found when comparing the elicited signal change in the left primary visual cortex to the one in the right primary visual cortex suggesting that even for functionally equivalent areas of the brain the hemodynamic response might be different at different points in time..

Keywords

BOLD, Nonlinearity, Short stimulus duration.

Submitted at: Nov. 15, 2006
Accepted at: March 15, 2007

Citation

I. MENDICHOVSZKY, A. FERRETTI, C. DEL GRATTA, M. CAULO, C. COSMA, G. L. ROMANI, Nonlinear effects in the bold response for short stimulus duration heterogeneity of hemodynamic response, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 3, pp. 795-798 (2007)