NAVIGATED BRAIN STIMULATION
Navigated Brain Stimulation provides maps of cortical functions for the
neurosurgeon and helps patients recover from depression or stroke, as
Janne Huhtala of Nexstim Oy explains
Pan European Networks: Science & Technology
06
152
PROFILE
N
avigated Brain Stimulation (NBS) from Nexstim is a
revolutionary, non-invasive neurostimulation technique.
In NBS, magnetic pulses applied over a patient’s head
lead to activation of underlying brain cells by the induction of
electric fields. NBS can be used to map the locations of motor or
speech functions on the brain cortex in planning for neurosurgery
or to treat the brain in various diseases.
Transcranial magnetic stimulation (TMS) has been studied for over
25 years and is well understood to be safe for patients. The
Nexstim NBS system adds location information to traditional TMS.
Thanks to MRI-based navigation and advanced modelling, the
NBS system is able to show precisely which area in the brain is
being stimulated with each pulse and to provide a known dose of
stimulation to an accurate anatomical location and direction with
full repeatability.
After linkage, the NBS system
operator sees the exact location of
the electric field generated by the
coil inside the patient’s brain. The
patient only needs to wear a
reflector headband to track head
movement. In this manner, Nexstim
makes invisible TMS visible.
NBS in presurgical planning
In patients diagnosed with brain tumour or epilepsy, NBS can be
used for creating a map of the brain’s vital functions, revealing
which parts of the brain are critical for the control of movement
and speech. Nexstim NBS maps are as accurate as those
obtained during surgery via direct stimulation of the cortex; the
gold standard. NBS information can be used in deciding on
treatment options and when planning a resection. NBS
information helps the neurosurgeon preserve the vital areas of the
brain while removing as much of the diseased tissue as possible.
An NBS mapping session is non-invasive, painless and can be
performed in 30-45 minutes.
Nexstim’s NBS system is CE-marked and has been cleared for
sales and marketing by the US FDA for functional mapping of
motor and speech cortices. Neurosurgical associations in the USA
and Germany have actively supported reimbursement for navigated
TMS in cortical mapping and surgery planning, and from January
2013, codes are now available
in both countries. The accuracy
and utility of Nexstim’s NBS has
been demonstrated in over 20
original articles, covering 339
patient cases.
Now that nine of the largest
neurosurgery departments in
Germany have adopted NBS, it
is becoming the new standard
of care for presurgical brain
mapping. In the USA, interest in
paediatric applications has
been high, with three centres acquiring NBS systems recently. In
total, 16 US institutions are using NBS.
How navigated brain stimulation works
When activated by the operator, a purpose-designed, focal coil
generates a brief magnetic field over the head. The magnetic field,
no stronger than that used in MRI, generates a small electric field
as it passes through the cortex. The operator adjusts the field so
that the coil activates only a small population of neurons.
Adjusting the field strength to the individual patient’s motor
threshold gives the NBS system the ability to finely differentiate
between areas of the cortex. Navigation is achieved by ‘linking’ the
shape of the patient’s head to the brain anatomy revealed by MRI.
After linkage, the NBS system operator sees the exact location of
the electric field generated by the coil inside the patient’s brain.
The patient only needs to wear a reflector headband to track head
movement. In this manner, Nexstim makes invisible TMS visible.
The NBS system uses EMG from the patient’s muscles in order to
localise the motor cortex in the brain. Surface electrodes attached
to the skin over muscles pick up the electrical signals the brain
sends when the motor cortex is stimulated. By observing multiple
EMG channels, the operator can also differentiate the areas
corresponding separately to individual muscles.
For locating areas of the brain vital for speech, the same principle of
induced electric field can be applied in a special way. By rapidly
stimulating a specific area of the cortex its normal function can be
temporarily disturbed.When an area of the brain vital for speech is
stimulated in this manner, the rapid stimulation can cause the
patient to hesitate, make mistakes or even be unable to voice a
word. Such an area can be considered to be involved in speech
production and needs to be preserved in surgery or other treatment.
Nexstim’s NBT can accurately and
repeatedly target stimulation to
the dorsolateral prefrontal
cortex of the brain, known to
have reduced activity in
depressed patients
NEURODEGENERATIVE RESEARCH
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