Brain implants
could control blood pressure
Shaoni Bhattacharya and Will Knight
An electrical current could one day
control high blood pressure in people, a new study suggests.
Short bursts of electrical stimulation
were applied in an area in the midbrain called the periaqueductal grey matter (PAG)
in 15 awake patients. The patients had already had the
deep brain electrodes fitted as a treatment for chronic pain.
The stimulation lowered blood pressure
in patients who had the electrodes near the front (or ventral) part of the PAG.
In patients where the electrodes were near the back (or dorsal) part, blood
pressure could be increased.
“It’s very early days yet, but this is
an exciting preliminary finding,” says Alexander Green, at the department of
neurosurgery,
But he cautions that the surgery to
place the electrodes in the brain carries a one in 300 risk of stroke. For
patients receiving the implants to treat severe conditions such as Parkinson’s
disease, the risk may be acceptable. But that is currently far from the case
for patients with blood pressure problems.
Fight or
flight
Previous experiments, dating back to
the 1930s, have exerted a degree of mind-control over animals by electrically
stimulating the PAG. Blood pressure changes and "freezing" responses
have been produced in cats, and stimulating the PAG of rats elicits a “defense”
response. Green speculates that the PAG may be involved in control of the
cardiovascular system and the "fight-or-flight" survival responses –
of which changes in blood pressure could be one part.
The team stimulated the patients’
brains for periods of about 5 minutes at a frequency of 10 Hertz, followed by a
3-minute recovery period. The electrode was about 1.2 millimeters in diameter
with four “contact points” at its end. These points are 1 mm apart and a current flows between them when switched on, Green
explained to New Scientist.
The researchers saw that the systolic
blood pressure dropped by an average of 14.2 millimeters of mercury (mmHg) – or
13.9% - in seven patients, in whom the ventral PAG had been stimulated. In six
patients, systolic blood pressure shot up by an average of 16.7 mmHg (16.4%),
after the dorsal PAG was stimulated.
Two of the patients who responded
showed both increases and decreases in blood pressure at different times, while
the remaining four people did not respond at all.
As well as potentially treating
hypertension (high blood pressure), Green says the technique might one day be
used to relieve a condition called postural hypotension – where a patient’s
blood pressure falls uncontrollably upon standing up.
Journal reference: Neuroreport
(vol 16, p 1741)
