Effects of variations in interstimulus interval on activation-flow coupling response and somatosensory evoked potentials with forepaw stimulation in the rat
Bm. Ances et al., Effects of variations in interstimulus interval on activation-flow coupling response and somatosensory evoked potentials with forepaw stimulation in the rat, J CEREBR B, 20(2), 2000, pp. 290-297
In functional neuroimaging studies, the hemody- namic response to functiona
l activation is used as a surrogate marker for neuronal activity, typically
in response to task paradigms that use periodic stimuli. With use of a mod
el system of electrical forepaw stimulation in rats (n = 14) with laser-Dop
pler (LD) monitoring of cerebral blood now (CBF) changes in the somatosenso
ry cortex, the effects of variations in the interstimulus interval (ISI) on
the hemodynamic response to periodic stimuli were examined. A characterist
ic peak flow response was seen for 4-second stimuli and a peak and plateau
response were seen for all 8-second stimuli regardless of LSI. However, bot
h the amplitude of the LDCBF response and the integrated response were sign
ificantly reduced fur shorter ISIs, whereas the baseline now was not altere
d. Somatosensory evoked potential responses were also recorded in some rats
(n = 8) and remained unchanged for the various ISIs for a particular stimu
lus duration. These results suggest that the decrease in the LDCBF response
s observed with shorter ISIs likely represents a refractoriness of the hemo
dynamic response and not neuronal function. These results may have importan
t implications for the optimization and interpretation of functional activa
tion paradigms that use periodic stimuli.