BOLD fMRI and somatosensory evoked potentials are well correlated over a broad range of frequency content of somatosensory stimulation of the rat forepaw

Abstract

Electrical stimulation of the rat paw is commonly used to study the hemodynamic, metabolic, and neuronal mechanisms of functional MRI (fMRI) responses in somatosensory cortex. Several groups have reported good correlation between the Blood Oxygenation Level Dependent (BOLD) fMRI signal and somatosensory evoked potentials (SEPs) using short, typically 300 μs, square stimulation pulses. The spectral power of these short pulses is evenly distributed over a wide range of frequencies and thus the effects of the frequency content of the stimulation pulse on fMRI responses have not been previously described. Here, the effects that different stimulation pulse waveforms with a range of frequency content have on neuronal activity, as measured by SEPs, and on the amplitude of the BOLD fMRI signal in rat somatosensory cortex are investigated. The peak-to-peak SEP amplitudes increased as the power in the high frequency harmonics of the different pulse waveforms increased, using either triangular or sinusoidal stimuli waveforms from 9 Hz to 180 Hz. Similarly, BOLD fMRI response increased with increased high frequency content of the stimulation pulse. There was a linear correlation between SEPs and BOLD fMRI over the full range of frequency content in the stimulations.

Comprehensive correlation between neuronal activity and spin-echo blood oxygenation level-dependent signals in the rat somatosensory cortex evoked by short electrical stimulations at various frequencies and currents

“…Therefore, it is essential to elucidate the relationship between BOLD signals and neuronal activity for interpreting the fMRI signals; this relationship has been investigated mainly by animal studies measuring evoked potentials as indices of the neuronal activity in the somatosensory cortex (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009). Although most of the human fMRI studies employ the event-related task design that has a short stimulus duration, animal studies generally investigate the relationship between BOLD signals and evoked potentials with a stimulus duration of several tens of seconds (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009). Unlike BOLD studies, numerous optical studies performed using laser Doppler flowmetry (LDF) (Ngai et al, 1999;Matsuura and Kanno, 2001;Ureshi et al, 2004Ureshi et al, , 2005 and optical imaging (Devor et al, 2003;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Hewson-Stoate et al, 2005;Martin et al, 2006) have investigated the hemodynamic responses such as CBF and deoxygenated hemoglobin changes to neuronal activity in the rat cortex with a short stimulus duration (2-5 s) (Matsuura and Kanno, 2001;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Ureshi et al, 2004Ureshi et al, , 2005Hewson-Stoate et al, 2005;Martin et al, 2006).…”

“…Furthermore, most of the optical studies performed using electrical stimulation varied either in frequency (Ngai et al, 1999;Matsuura and Kanno, 2001;Martindale et al, 2003; -3 - while maintaining a fixed current strength (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009), and few fMRI studies have comprehensively investigated this relationship at different stimulus frequencies and currents.…”

“…Animal fMRI studies on somatosensory activation investigated the relationship between BOLD signals and neuronal activities by changing the stimulus frequency while maintaining a fixed current strength (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009), and few fMRI studies have comprehensively investigated this relationship at different stimulus frequencies and currents.…”

“…Thus, fMRI is an indirect method for assessing neuronal activity. Therefore, it is essential to elucidate the relationship between BOLD signals and neuronal activity for interpreting the fMRI signals; this relationship has been investigated mainly by animal studies measuring evoked potentials as indices of the neuronal activity in the somatosensory cortex (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009). Although most of the human fMRI studies employ the event-related task design that has a short stimulus duration, animal studies generally investigate the relationship between BOLD signals and evoked potentials with a stimulus duration of several tens of seconds (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009).…”

“…Unlike BOLD studies, numerous optical studies performed using laser Doppler flowmetry (LDF) (Ngai et al, 1999;Matsuura and Kanno, 2001;Ureshi et al, 2004Ureshi et al, , 2005 and optical imaging (Devor et al, 2003;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Hewson-Stoate et al, 2005;Martin et al, 2006) have investigated the hemodynamic responses such as CBF and deoxygenated hemoglobin changes to neuronal activity in the rat cortex with a short stimulus duration (2-5 s) (Matsuura and Kanno, 2001;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Ureshi et al, 2004Ureshi et al, , 2005Hewson-Stoate et al, 2005;Martin et al, 2006). Thus, an animal fMRI study with short stimulus duration is expected to bridge the results of the optical studies using short stimulus durations and those of the BOLD studies using long stimulus durations.Furthermore, most of the optical studies performed using electrical stimulation varied either in frequency (Ngai et al, 1999;Matsuura and Kanno, 2001;Martindale et al, 2003; -3 - while maintaining a fixed current strength (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009), and few fMRI studies have comprehensively investigated this relationship at different stimulus frequencies and currents.Thus, the present study aimed to investigate the relationship between BOLD signals and neuronal activities in the somatosensory cortex of anesthetized rats for forepaw electrical stimulation at a short duration of 4 s by changing both frequencies (1-10 Hz) and currents (0.5-2.0 mA). BOLD signals with a spin-echo echo planar imagining (EPI) sequence at 7 T and scalp-based somatosensory evoked potentials (SEP) were obtained from individual rats.…”