Biomedical Engineering Reference
In-Depth Information
composed of multiple whiskers (Friedberg et al.,
2004; Veinante & Deschênes 1999). In contrast,
Sp5 thalamic neurons typically respond to more
than four whiskers, and thus have larger RFs
(Friedberg et al., 2004; Woolston et al., 1982).
Thus, at the single-neuron level, there is a high
degree of integration of tactile inputs from multiple
whiskers in most trigeminal neurons.
In the contralateral thalamus (VPm) the infor-
mation from the barrelettes is received by groups
of neurons that are called berreloids (Sugitani et
al., 1990). The sensory information arrives through
the lemniscal pathway. Moreover, the paralemnis-
cal pathway transports less precise information
from Sp5 neurons to the contralateral posterior
thalamic nucleus (Po), and also to VPm (Patrick
& Robinson, 1987).
There is also a similar organization in the pri-
mary somatosensory (SI) cortex. The information
of the vibrissae is organized in columns called
barrels and each barrel receives information from
a single or few vibrissae (Erzurumlu & Jhaveri,
1990; Hutson & Masterton, 1986).
There is also a feed-back projection from SI
(and also from the primary motor cortex) to the
trigeminal nuclei. This is a monosynaptic crossed
projection going by the pyramidal tract with an
extremely precise somatotopy (Dunn & Tolbert,
1982). The electrophysiological properties and
the action of this projection are currently less
known. Making a parallel, in the dorsal column
nuclei this projection has shown to be relevant to
modulation of somatosensory responses, being
able to modify the sizes of the RF and increasing
the acuity of the system (Malmierca & Nuñez,
1998, 2004, 2007; Mariño et al., 2000).
the trigeminal complex that control the RF size.
GABAA antagonists increase the size of the
RFs at the trigeminal nuclei, while the agonists
reduce it (Takeda et al., 2000). Also glycinergic
interneurons have been shown to inhibit the so-
matosensory responses at the trigeminal complex
(Ressot et al., 2001).
Barrelette cells exhibit a monosynaptic EPSP
followed by a disynaptic IPSP after stimulation of
the trigeminal nerve. The disynaptic IPSP should
be mediated by a feed-forward inhibitory circuit.
GABAergic cells in the Pr5 most likely serve
as inhibitory interneurons in this feed-forward
circuit. An IPSP without the preceding EPSP
can be evoked in barrelette cells by stimulating
the trigeminal nerve, suggesting that there is a
separate inhibitory circuit other than the feed-for-
ward inhibitory circuit (Lo et al., 1999). Synaptic
plasticity has been also described in the trigeminal
complex. At day 1 after born (P1) when barrelettes
are in their formative stage, high frequency stimu-
lation of trigeminal ganglion afferents produces a
long-term depression (LTD) in synaptic responses.
Between P3-7 when barrelettes are consolidat-
ing, heightened activity of trigeminal ganglion
axons leads to long-term potentiation (LTP) of
the responses (Guido et al., 2004). This suggests
that LTD can serve as a mechanism selectively
eliminating multiple whisker inputs and LTP to
consolidate inputs that are connecting.
Mathematical Tools to Analyze
Neuronal Activity
Extracellular electrophysiological study of the
neural activity results in simultaneous observation
of several processes, e.g. tactile stimulation-neu-
ral response. Then the recorded activity can be
considered as a multivariate process, where the
variables available for analysis are the times of
occurrence of spikes or local field potential. To
address spike trains several statistical techniques
to infer on the neuronal interaction have been
developed both in time and in frequency domains.
Synaptic Properties of Trigeminal
Neurons
The peripheral and corticofugal inputs to tri-
geminal nuclei are glutamatergic (Feliciano &
Potashner, 1995). There are also electrophysi-
ological evidences of GABAergic activity within
Search WWH ::
Custom Search