Biomedical Engineering Reference
In-Depth Information
blood flow), achieved with different sensory paradigms and dis-
cuss similarities and/or differences across the different sensory
systems as well as the potential advantages they may have for the
study of different neuroscientific questions.
The mammalian brain functions in a world full of sensory
cues. The nature of stimuli perturbing the different sensory
domains is quite diverse - from odorant molecules at the nose
epithelium and photons bombarding the retina, to vibrations
of the eardrum and mechanoreceptors on the skin. As a con-
sequence, the brain structures dedicated to different senses are
anatomically distinct, from the level of cell types to their vast
synaptic interconnections
(32)
. Therefore, different peripheral
stimuli of the rodent brain offer a rich platform on which to test
effects of perturbations on functionally and anatomically hetero-
geneous populations of neural tissues. In addition, the vast litera-
ture on rodent brain anatomy, morphology, and physiology make
possible viable extrapolation of results from such experiments.
Since the physical world around any creature impinges on all
its sensory systems in parallel, a multi-dimensional representation
of the surroundings is thereby needed for complex (e.g., hunting
for prey) and even simple (e.g., avoidance of noxious conditions)
behaviors. A central hypothesis in the design of controlled fMRI
and neurophysiologic studies, as described here and executed sim-
ilarly in many other laboratories around the world, is that sen-
sory stimuli may have very different neurophysiologic outcome(s)
when paired with a near simultaneous event in another modality.
The different sensory paradigms described here may be applied
directly to the study of multi-sensory interactions in anesthetized
rats
(33)
and elucidation of such effects with high spatiotemporal
precision is hypothesized to contribute to the understanding of
the awake functioning brain
(34)
.
2. Materials and
Methods
The design principle of our approach for reproducible stimulation
of multiple senses can be summarized with the word
modularity
.
The different sensory systems we aim to probe clearly necessi-
tate specialized stimulus delivery systems, operating at appropriate
timescales. However care was taken not to build mutually exclu-
sive apparatus for the different senses (i.e., one stimulus modal-
ity should not prevent concurrent or simultaneous application of
another). The basic requirement of accurate dynamic control over
the stimuli called for computerized implementation. Therefore,
all of our designs are based on a CED
1401 analog-to-digital
converter unit (or CED unit), in particular, its programmable
analog and digital output capabilities, controlled by custom-
μ
