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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