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Mapping cerebral hemodynamics of the human motor
cortex by multi-channel time-resolved
near-infrared spectroscopy
L. Craighero, L. Fadiga Università di Ferrara
Dip. SBTA, Sezione di Fisiologia Umana, via
Fossato di Mortara 17/19, I-44100 Ferrara,
Italy A. Torricelli, D. Contini, A. Pifferi, L.
Spinelli and R. Cubeddu ULTRAS-CNR-INFM and
IFN-CNR, Politecnico di Milano, Dipartimento di
Fisica, Piazza Leonardo da Vinci 32, I-20133
Milano, Italy
ABSTRACT The aim of the research was to
investigate the spatial resolution of a
time-resolved system for functional near-infrared
spectroscopy (NIRS) during a motor task. Results
showed that the system is able to discriminate
both the antero-posterior extension of
hand-related motor activation and the
medio-lateral somatotopy of hand and shoulder
motor representations.
TASK 1 antero-posterior extension of the right
hand motor representation
HHb - deoxyhemoglobin O2Hb - oxyhemoglobin THb
- total hemoglobin SO2 - of oxygen
saturation
DHHb -1.0 / 1.0 mM DO2Hb -1.5 / 1.5 mM DtHb
-2.5 / 2.5 mM DSO2 -1.5 / 1.5 mM
Baseline 0-20 s Task 20-40
s Recovery 40-80 s
Blue asterisk indicates the right hand hot spot
location (left hemisphere) as assessed by TMS in
the subject according to the method described by
Fadiga et al. 5.
INTRODUCTION The problem of mapping functional
activation in the human brain by optical
radiation is challenging. The diffusive nature of
biological tissues prevents the discrimination of
absorption and scattering contributions by simple
continuous wave techniques. Time domain
techniques, on the contrary, are able to
discriminate between them and to derive absolute
values for the hemodynamic parameters in a real
heterogeneous medium like the human head 1.
Moreover, relevant studies have shown that in the
time domain depth sensitivity can be improved by
simply exploiting the temporal information 2-4.
Here, we investigated the spatial resolution of a
dual wavelength (690 and 820 nm) multi-channel
time-resolved system for functional NIRS in the
study of the antero-posterior extension of
hand-related motor activation, and of the
medio-lateral somatotopy of hand and shoulder
motor representations.
Baseline
medial
anterior
posterior
hand
lateral
Task (finger tapping)
METHODS One right handed normal subject
participated to the experiment. During a
preliminary mapping session, right hand and
shoulder motor representations were assessed by
using transcranial magnetic stimulation (TMS)
5. The experimental session was subdivided into
two tasks. The first task was aiming at
investigating the antero-posterior extension of
the right hand motor representation as detected
by NIRS. A specially designed probe (4 source
fibers and 10 collecting bundles,
source-collector relative distance rho2.0 cm),
was placed over the right hand motor
representation of the left hemisphere,
perpendicularly to the central sulcus. The
protocol consisted of 20 s baseline, 20 s right
hand motor activity (Lurias finger tapping), and
40 s recovery. The protocol was repeated 10 times
in order to increase the signal-to-noise ratio by
block averaging. The acquisition rate was 1 s.
The second task was designed to test the
somatotopic representation of hand and shoulder
motor representations by using a protocol similar
to that of the previous task. The probe was
placed over the shoulder/hand motor
representations of the left hemisphere, along the
central sulcus. The protocol consisted of 15 s
baseline, 15 s right hand finger tapping or right
shoulder rotation (randomized and executed
according to visual instructions), and 30 s
recovery. The protocol for each type of movement
was repeated 5 times. The acquisition rate was 1
s. The analysis was restricted to the superior
part of the probe (indicated by the yellow circle
in the figure) since it was our region of
interest.
Spatial maps of HHb, O2Hb, THb, and SO2
concentration changes, separately presented for
the baseline and task experimental phases (10
times block averaging).
Average (10 trials) cerebral blood oxygenation
changes in each of the 16 channels during the
course of the experiment. The ordinates indicate
the concentration changes of O2Hb (red line), HHb
(blue line), tHb (purple line), and SO2 (green
line). Dotted lines indicate the different phases
of the experiment 20 s baseline, 20 s task, and
40 s recovery, during time.
DHHb and DO2Hb during single trials (i.e. no
block averaging) collected by a single couple of
emitters-collectors during the finger tapping
task.
shoulder
TASK 2 somatotopic representation of hand and
shoulder motor representations.
Baseline 0-15 s Task 15-30
s Recovery 30-60 s
shoulder
Baseline
Task
hand
Baseline
Task
CONCLUSIONS In conclusion, a multi-channel
time-resolved system for functional NIRS has been
successfully employed to study hemodynamic
response following motor activity in the adult
brain. In addition, the system was able to
discriminate the antero-posterior extension of
hand-related motor activation and the somatotopy
of hand and shoulder motor representations.
Moreover, the system used in the present study is
sensitive enough to significantly determine
cortical motor activation in single trials. In
the light of brain-machine interfaces, this
capability gives new potentialities to NIRS
recording of regional blood flow. 1. F.
Martelli, S. Del Bianco and G. Zaccanti,
Perturbation model for light propagation through
diffusive layered media, Phys. Med. Biol. 50,
2159-2166 (2005). 2. H. Steinbrink, H. Wabnitz,
A. Obrig, Villringer and H. Rinneberg,
Determining changes in NIR absorption using a
layered model of the human head, Phys. Med.
Biol. 46, 879-896 (2001). 3. S. Del Bianco, F.
Martelli and G. Zaccanti Penetration depth of
light re-emitted by a diffusive medium
theoretical and experimental investigation,
Phys. Med. Biol. 47, 4131-44 (2002). 4. J. Selb,
J. J. Stott, M. A. Franceschini, A. G. Sorensen,
and D. A. Boas, Improved sensitivity to cerebral
hemodynamics during brain activation with a
time-gated optical system analytical model and
experimental validation, J. Biomed Opt. 10,
11013 (2005). 5. L. Fadiga, L. Fogassi, G.
Pavesi and G. Rizzolatti Motor facilitation
during action observation a magnetic stimulation
study, J. Neurophysiol. 73, 2608-2611 (1995).

• RESULTS
• Task 1 antero-posterior extension of the right
  hand motor representation.
• Data showed a focal increase of O2Hb and the
  corresponding decrease of HHb in the channels
  placed over the hand motor representation hot
  spot, determined by TMS.
• Task 2 somatotopic representation of hand and
  shoulder motor representations.
• Data showed a differential activation for finger
  and shoulder movements.