NEWS: Probing the brain wirelessly
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IR-absorbing lead selenide particles form the basis of a method for the
study of neuronal activation in samples of brain tissues without the need for
hard-wired electrodes. The technique instead utilises light-triggered
nanostructured semiconductor photoelectrodes to probe activity. Philip Larimer, Richard Todd Pressler, and Ben Strowbridge of the Department
of Neurosciences, at Case Western Reserve University, in Cleveland, Ohio,
working with Yixin Zhao and Clemens Burda in CWRU's Center for Chemical
Dynamics and Nanomaterials Research explain their approach in the current
issue of Angewandte Chemie. Understanding brain function remains one of the great challenges facing
science. For example, simply understanding how brain regions process synaptic
inputs to generate defined responses is a puzzle. One particularly promising avenue of research in this area remains the
study of the electrical conduction of stimuli by nerve cells, neurons.
However, in order to study neuronal circuits in detail, a sharp metal
electrode is usually introduced into the living brain or a brain slice to
introduce a current. Such a crude approach is too blunt a probe to discern
the highly complex activation patterns of natural nerve stimuli. Moreover,
this approach causes direct damage to tissue because of unwanted
electrochemical side reactions. Alternative approaches involve genetically encoded light switches or
bath-applied caged compounds for neuronal stimulation, all of which add a
layer of complexity to any given experiment. Now, neuroscientists and nanomaterials researchers at CWRU have developed
an approach that is infinitely gentler on the tissue being probed and elicits
a more natural response from nerve impulses. The approach is based on a
micropipette coated with semiconductor nanoparticles (composed of PbSe). PbSe
is a Group IV-Group VI semiconductor with a narrow bulk band-gap energy of
just 0.26 electronVolts, the researchers explain; as such it is commonly used
in infrared photodetectors. The team characterised their PbSe films using scanning electron microscopy
(SEM) and X-ray diffraction (XRD), with the crystal structure results
revealing it to have the rock salt structure known for bulk PbSe. Stimulating PbSe with IR light allows them to activate neurons in brain
tissue with visible or infrared (IR) light. In contrast to conventional
electrodes, these new photoelectrodes require neither wires nor electrical
power. "With these photoelectrodes, no molecular biology manipulations are
necessary, and no direct contact of the neurons with nanoparticle-coated
surfaces is required (with the inside-coated tips)," the researchers
say. The team led by Strowbridge and Burda coated the interior of extremely
finely drawn-out glass micropipettes with lead selenide nanoparticles. Short
bursts of laser light can be used to create an electrical pulse in the
micropipette which the researchers then use to stimulate neurons in rat brain
samples. The use of a laser pulse to generate the stimulating electrical
field means that a high degree of temporal resolution is possible. The
researchers add that this could allow them to record the natural activation
patterns of very similar nerve impulses. The researchers hope their new
photoelectrodes will allow researchers to study cooperation of neurons. They have now tested their wireless probes on the olfactory bulb. This is
a region of the brain involved in processing smell. The neurobiology of the
olfactory bulb is especially intriguing because it utilises unusual synaptic
connections the physiological role in facilitating olfactory discrimination
and learning are yet to be revealed. They have also probed the hippocampus, a
part of the cerebrum important in the transfer of contents from short-term to
the long-term memory. The team is particularly interested in its so-called
"mossy" cells which are thought to have a connection with epilepsy.
They saw no toxicity problems nor damage to neurons even after repeated
stimulation. Additional work could also point the way to therapeutic applications where
the wireless probes might be used to activate individual regions of the
brain, stimulate damaged or cut nerves and perhaps restore function, without
the need for electrical wiring. Related links: |
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