Biomedical Engineering Reference
In-Depth Information
Table 3.1 Mean MTs with standard deviations (denoted
) in relation to the coil orientation for
both sessions
Session 1 Session 2
0
20
30
40
50
60
80
160
180
200
210
220
230
240
260
66 59.3 54.6 57.3 57.4 60 61.5 60.25 57.6 54.4 53.8 54.8 56.4 58.6 64
19.4
15.6
14.9
13.6
17.2
15.4
17.0
21.1
16.0
17.9
17.7
21.3
23.9
26.7
29.8
The MTs are presented in % of MSO
11
:
8
10
:
8 % of MSO and 8
:
0
5
:
9 % of MSO for sessions 1 and 2, respectively.
This difference in motor threshold amplitude is significant for session 1 (p
¼
0
:
04)
and session 2 (p
¼
0
:
02).
After fitting the average recordings to the model sinusoidal, the resulting curve
has the form:
MT
ð
a
Þ¼
63
:
3
7
:
3
cos
ð
2
a
þ
72
:
1
Þþ
4
:
7
cos
ð
a
31
:
2
Þ
:
ð
3
:
3
Þ
The coefficient of determination, R
2
, of the sinusoidal fitting is 0.86 which is
significant at the 0.01 level (p \ 0
:
01). The average R
2
for each subject is
0
:
88
0
:
05. On average, the sinusoidal minimum is located at 35
:
2
and 214
:
9
with SDs of 26
:
5
and 16
:
8
for session 1 and 2, respectively.
Figure
3.4
shows the computed sinusoidal curve for subject 'Ch' as an example.
The sinusoid smoothly fits the recordings as expected. The local minimum
opposite to the optimal orientation is slightly larger than the global minimum.
The estimated orientation of the gyrus underneath the hot-spot estimated in the
MRI scans is presented in Table
3.2
. Additionally, the estimated optimal coil
orientation angles are shown for the subjects. The correlation coefficient (Pear-
son's r) between angle of the precentral gyrus and the optimal coil orientation is
0
:
78. The correlation is therefore significant at the 0.05 level (p \ 0
:
05). Note that
for comparison the optimal coil rotation must be subtracted by 180
.
Fig. 3.4 The motor threshold
recordings for both sessions
of subject 'Ch'. A sinusoidal
curve (dotted line) was fitted
to the recordings. The global
minimum at the optimal coil
orientation is smaller than the
local minimum at the opposite
coil orientation. The standard
coil orientation (at 180
),
however, is clearly not
optimal
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