Tactile and Non-tactile Sensory Paradigms for fMRI and Neurophysiologic Studies in Rodents - Dynamic Brain Imaging - page 216

were stimulated simultaneously. Given prior information about
contralateral S1 BF activation (59-61) , we hypothesize that the
number of barrels corresponded approximately with the number
of whiskers stimulated. The robust and reproducible contralateral
S1 BF activation was probably improved because whiskers on the
ipsilateral side were clipped to remove spurious artifacts.
The averaged BOLD response with 8 Hz whisker stimula-
tion ( Fig. 10.5B ) from the contralateral S1 BF (

∼

4%) was in good
agreement with prior findings under similar experimental condi-
tions (25, 62) . While the BOLD response was sustained for the
duration of the stimulus, the signal usually decreased towards
the pre-stimulus baseline as soon as the stimulus was termi-
nated. In the same subject, we have used 30 s and 120 s dura-
tion stimuli and observed sustained BOLD response (data not
shown). Localized S1 BF measurements of CBF ( Fig. 10.5C )and
MUA ( Fig. 10.5D ) were well correlated with the fMRI results.
Increasing the stimulation frequency augmented the BOLD
response in the contralateral S1 BF ( Fig. 10.6 ). In the same sub-
ject, the BOLD response for 12 Hz stimulation was nearly twice
the magnitude of the response for 4 Hz stimulation (63) .

3.4. Forepaw
Stimulation

We evaluated forepaw stimulation induced activity patterns in
the somatosensory area ( Figs. 10.7 and 10.8) . There were no
stimulation-induced variations in systemic physiology for forepaw
stimulation amplitudes of less than 5 mA and frequencies of less
than 40 Hz (data not shown). Electrical stimulation (2 mA, 3
Hz) of the forepaw with 0.3 ms duration pulses for 30 s evoked
a strong positive BOLD signal change in the contralateral, pri-
mary somatosensory area of the forelimb (S1 FL ). No signifi-
cant BOLD signal changes were observed in the ipsilateral S1 FL
region during unilateral forepaw stimulation. In a given subject,
when either the left or the right forepaw was concurrently stimu-
lated, there were no significant differences in the BOLD response
between the two S1 FL regions ( Fig. 10.7A) . The intra-subject
reproducibility of BOLD activations with either forepaw stim-
ulation ( Fig. 10.7A,B ) was nearly indistinguishable from the
inter-subject reproducibility of BOLD activations ( Fig. 10.7C ),
as assessed by the number of significantly activated pixels in the
S1 FL region and/or the averaged BOLD signal change in the S1 FL
region (data not shown). These results are in good agreement
with prior fMRI observations (16, 24) .
The averaged BOLD response with 3 Hz forepaw stimula-
tion ( Fig. 10.8A ) from the contralateral S1 FL ( 8%) was in good

agreement with prior findings under similar experimental condi-
tions (16, 24) . The BOLD response was sustained for the dura-
tion of the 30-s stimulus ( Fig. 10.8A ) and even when the stim-
ulus duration was lengthened to several minutes ( Fig. 10.8B) .
Increasing the stimulation frequency above 3 Hz decreased the

∼