Supplementary Information (SI) Appendix:
Supplementary I:
Setup of EEG and LDF probes on the cortex (A) and forepaw stimulation paradigm (B)
A)
B)
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Fig.s1 Panel A: Experimental setup of the probes and the thickness of the thinned skull over the cortex.
(A0) Illustration of EEG and LDF probes; (A1) White-light surface image of the thinned skull; (A2)
Projection of 3D blood flow image using optical coherence Doppler tomography in cortex areas with
and without thinning the bone; (A3) 2D cross-sectional optical coherence tomography image to show
the skull (~95m) thickness over the cortex. Panel B: Forepaw stimulation paradigm and data
analysis. (B0) Forepaw stimulation: 10s duration with 3Hz, 2mA bipolar pulse train; (B1) EEG
quantification: nrest, Nsep to measure synchronized neuronal activity counts during resting state
(counts/minute) and forepaw stimulation state (counts), respectively, and VSEP to measure the average
field-potential spike intensity evoked by forepaw stimulation; (B2) CBF quantification: CBF0 for
resting-state level (a.u.), ∆CBFp and ∆CBFt for relative peak change and relative accumulated (i.e.
average) change by forepaw stimulation.
It was previously noted that, although forepaw electrical stimulation forces the neuronal activity to be
synchronized (e.g., NSEP 3Hz), it does not necessarily increase the field potential amplitude as
compared to that of the resting state. (Zhao F, et. al., BOLD study of stimulation-induced neural
activity and resting-state connectivity in medetomidine-sedated rat. Neuroimage 39:248-260, 2008)
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Supplementary II:
Physiological parameters (i.e., MABP, pCO2, and HBR) during the experiments
The mean arterial blood pressure (MABP), pCO2 and heart beat rate (HBR) were recorded throughout
the experiments to ensure that their values were within the range for physiological autoregulatory
responses. Table s1 summaries the mean MABP, the pCO2 and HBR changes of the cocaine animals
(n=5) as a function of time. It indicates that cocaine administration induced a brief increase in MABP
from 108±2.8 mmHg to 123±3.7 mmHg within 3-6min after cocaine injection that was sustained at
124-125 mmHg till 30min post cocaine, indicative of cocaine inducing mild hypertension (p=0.006).
Nevertheless, the MABP values of 100-125 mmHg were within the range for cerebral autoregulation.
In addition, there was no significant change in HBR before and after cocaine administration (p=0.885,
One Way RM ANOVA) and the pCO2 values were unchanged after cocaine (Table s1). These results
indicate that the decreases of CBF, CBF0 as well as the spontaneous neuronal activity (nrest) after
cocaine were independent of the physiological changes during the experiment, thus implying the
changes in CBF, CBF0, nrest were resulted from the effect of cocaine.
Table s1 Physiological recording of MABP, pCO2 and HBR
Time
Point
MABP
(mmHg)
pCO2
(mmHg)
HBR
(BPM)
Baseline
108±2.8
41.8±1.4
284±21.
2
3
6
9
12
15
18
21
24
27
30
min
min
min
min
min
min
min
min
min
min
122±3.
0
41.5±1.
3
283.2±
23.1
123±3.
7
40.8±1.
9
287.0±
19.7
119±2.
2
119±2.
1
42.5±0.
7
295.6±
14.7
124±3.
8
125±4.
3
42.3±1.
4
289.0±
17.8
124±4.
0
42.5±1.
0
286.4±
18.5
126±4.
6
42.3±1.
3
292.0±
16.2
124±3.
7
125±3.
6
42.3±0.
9
286.8±
16.3
42±1.2
291.4±
17.7
42±1.2
288.2±
18.9
42±1.6
290.4±
14.7
* MABP: mean artery blood pressure
* pCO2: partial pressure of carbon dioxide
* HBR: heart beat rate (BPM, beats per minute)
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Supplementary III:
Comparison of LFP, ECoG and EEG signals in response to electrical forepaw stimulation
Fig.s2 Comparison of LFP, ECoG and EEG signals. Forepaw electrical stimuli were delivered at 3Hz,
2mA with 0.3ms pulse width for all three groups. (a) Local field potential (LFP), which was previously
recorded from 0.6mm underneath the brain surface (roughly layer III-IV of the somatosensory cortex)
using a 0.127mm tungsten electrode, bandpass filtered from 0.3kHz to 3kHz and digitized at 20kHz
(Du et al., Journal of Innovative Optical Health Sciences, 2(2):1-12, 2009); (a’) A close-up view of a
single stimulation-evoked LFP spike from (a), indicating a pulse duration of 30-40ms. (b) ECoG signal
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recorded on the exposed cortex, using a 0.3mm tungsten electrode, bandpass filtered from 0.1Hz to
35Hz and digitized at 2kHz; (b’) A close-up view of a single stimulation-evoked ECoG spike from
(b), indicating a pulse duration of 60ms. (c) EEG signal recorded on the thinned skull of the cortex
by using a 0.3mm tungsten electrode, bandpass filtered from 0.1Hz to 35Hz and digitized at 2kHz;
(c’) A close-up view of a single stimulation-evoked EEG spike from (c), indicating a pulse duration
of 80ms.
A comparison of forepaw stimulation evoked LFP, ECoG and EEG signals indicates: 1) similar to the
LFP and ECoG measurements, the thinned-bone EEG recording employed in this study enabled us to
detect all 30 pluses in response to 30 forepaw electrical stimulations during the 10s stimulation
paradigm (i.e., 3Hz); 2) both EEG and ECoG recordings showed similar pulse transients to the pulse
transient recorded with LFP from within the layer III-IV of the cortex, although their amplitudes were
different depending on the signal amplifiers employed in the electrical circuits; 3) the pulse latencies
of measured by EEG and ECoG were 80ms and 60ms, respectively, which were broader than the
pulse duration of 20-40ms measured by LFP. Overall, these results indicate that our EEG measurement
observed from the thinned skull reflects the local field potential changes resulting from the neuronal
activity in response to the forepaw electrical stimulation.
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Supplementary IV:
Individual field potential signals between controls and cocaine animals
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Fig.s3 Typical EEG (field potential) signals observed from the individual animals in the control group
(upper panels) and in the cocaine group (lower panels). Upper panels: EEG traces from 3 animals in
the control group before (a1, a2, a3) and after (a1’, a2’, a3’) saline administration, and their superposed
resting-state power spectral density (PSD) curves before (a4) and after (a4') saline administration.
Lower panels: EEG traces from 3 animals in the cocaine group before (b1, b2, b3) and after (b1’, b2’,
b3’) cocaine administration, and their superposed resting-state PSD curves before (b4) and after (b4')
cocaine administration. The resting-state PSD curves (a4, a4’, b4, b4’) are acquired excluding the
stimulation epochs.
Fig.s3(a4, a4') shows that there was no significant change in the resting-state spontaneous EEG spectral
power density before and after saline administration (p=0.94, n=5). However, Fig.s3(b4, b4') show that
there was a significant decrease in the resting-state spontaneous EEG power spectral density after
acute cocaine (p<0.01, n=5).
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Supplementary V:
Spontaneous neuronal activity (nrest) under different anesthesia
Fig.s4 Spontaneous neuronal activity under three different doses of α-chloralose, i.e., 25-, 32.5- and
50-mg/kg/hr, respectively. Blue traces: Spontaneous EEG traces with 10min recording for each of the
3 α-chloralose doses (red traces); Black bar curves: mean spike counts per minute for the 3 αchloralose doses, indicating no significant difference in the spontaneous neuronal activity (p=0.413,
One Way RM ANOVA). These results are consistent with previous reports (e.g., Lu et al,
Synchronized delta oscillations correlate with the resting-state functional MRI signal, PNAS 2007;
104(46): 18265-18269), showing no significant difference in the EEG spectra under different αchloralose doses (30-, 70-, and 100-mg/kg).
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