Long duration stimuli and nonlinearities in the neural-haemodynamic coupling

• Published in: Journal of cerebral blood flow and metabolism Vol. 25; no. 5; pp. 651 - 661
• Main Authors: Martindale, John, Berwick, Jason, Martin, Chris, Kong, Yazhuo, Zheng, Ying, Mayhew, John
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01-05-2005; Lippincott Williams & Wilkins; Sage Publications Ltd
• Subjects: Algorithms; Animals; Biological and medical sciences; Brain - blood supply; Brain - physiology; Cerebrovascular Circulation - physiology; Ear, auditive nerve, cochleovestibular tract, facial nerve: diseases, semeiology; Electric Stimulation; Gabaergic and benzodiazepinic system; Hemodynamics - physiology; Image Processing, Computer-Assisted; Laser-Doppler Flowmetry; Medical sciences; Models, Neurological; Neurology; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Non tumoral diseases; Otorhinolaryngology. Stomatology; Pharmacology. Drug treatments; Rats; Time Factors; Vascular diseases and vascular malformations of the nervous system; Vibrissae - innervation; impulse response; rat; laser Doppler flowmetry; nonlinear; current source density; haemodynamics; Doppler ultrasound study; Nervous system diseases; Rat; Rodentia; Cerebral disorder; Vertebrata; Mammalia; Animal; Central nervous system disease; Laser; Hemodynamics; Flowmetry; Cerebrovascular disease
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1038/sj.jcbfm.9600060

Recent studies have shown that the haemodynamic responses to brief (<2 secs) stimuli can be well characterised as a linear convolution of neural activity with a suitable haemodynamic impulse response. In this paper, we show that the linear convolution model cannot predict measurements of blood flow responses to stimuli of longer duration (>2 secs), regardless of the impulse response function chosen. Modifying the linear convolution scheme to a nonlinear convolution scheme was found to provide a good prediction of the observed data. Whereas several studies have found a nonlinear coupling between stimulus input and blood flow responses, the current modelling scheme uses neural activity as an input, and thus implies nonlinearity in the coupling between neural activity and blood flow responses. Neural activity was assessed by current source density analysis of depth-resolved evoked field potentials, while blood flow responses were measured using laser Doppler flowmetry. All measurements were made in rat whisker barrel cortex after electrical stimulation of the whisker pad for 1 to 16 secs at 5 Hz and 1.2 mA (individual pulse width 0.3 ms).