In this new research line, led by Luc Gentet, we focus on the neocortical neuronal circuits
involved in the processing of incoming sensory information, especially in the tactile and visual modalities.
Various advanced techniques are employed to this end, including in vivo whole-cell patch clamp recordings,
optogenetics and in vivo 2-photon calcium-imaging in the awake and behaving states.
Which type of cells are crucial for generating percepts that enable the animal to make behavioral decisions?
How does the brain combine tactile and visual information to forge integrated, multimodal percepts?
The diversity of cortical inhibitory interneurons is well established, yet little is known about its functional significance. In order to better understand neural computation at the local circuit level, it is essential to determine the role that each interneuronal subtype may play in shaping its response to sensory input. The primary visual cortex and somatosensory cortex are ideal systems for dissecting cell-specific roles in cortical information due to their clear circuitry in terms of orientation, spatial and frequency tuning and specific columnar organisation.
Example traces of simultaneous whole-cell recordings between a pair of excitatory layer2/3 pyramidal cell
(PYR, black)
and a fast-spiking interneuron (FS, red),
together with the anatomical reconstruction of their respective somatodendritic arborisations (left)
and membrane potential cross-correlogram (right) .
The membrane potentials of both cells were highly correlated despite their different cellular identities
GABAergic neurons, while forming approximately 10-15% of the neuronal cortical population in somatosensory layer 2/3
play a crucial role in maintaining the balance between excitation and inhibition. Recently, we have discovered that
their intrinsic firing rate is roughly an order of magnitude higher than pyramidal cells and that interneurons,
in their broad sense, display slow subthreshold membrane oscillations that are highly correlated with the activity
of nearby regular-spiking excitatory layer 2/3 pyramidal cells (Figure 1), indicating that they are not responsible
for the establishment of slow-wave oscillations at the local circuit level.
Actually, the contribution of interneurons
to cortical processing under different brain states is dependent upon their specific subtypes. We have shown that the
firing rate of fast-spiking interneurons decreased, and that of non-fast spiking inhibitory neurons increased, during
episodes of free whisking, a defined brain state in the awake animal (Gentet et al., 2010).
While we have classified three broad families to date (Somatostatin-positive cells, Fast-spiking cells, Non-fast-spiking
interneurons), the diversity of interneuronal subtypes implies that more specific interneuron classes may play crucial
roles in the shaping of specialised cortical functions, both in supragranular and in deeper cortical layers.
Using advanced optical and electrophysiological techniques combined with behavioural training,
we will investigate the function of GABAergic cells in sensory processing at the level of the neocortex.
Example anatomical reconstructions of axonal (coloured) and somatodendritic arborisations (black)
of layer2/3 GABAergic neurons classified according to their genetic and/or electrophysiological properties
(left)
together with a representative excitatory pyramidal cell (right).
Neuroanatomical reconstructions allow identification of precise cell types
in the complex circuitry involved in sensory integration
Our percept of our surrounding environment is built on the continuous integration of multiple streams of
sensory information. Understanding how different sensory modalities converge to form such a percept is a
crucial endeavour in modern neuroscience.
Several neocortical areas of interest have been identified where such multisensory intergration could take place,
including subpopulations of cells in primary sensory cortices. Because multisensory integration at the single-cell
level is likely to involve subtle subthreshold membrane potential changes, our methodology will allow us to attain
the level of precision required to observe such phenomena.
In particular, we will investigate the impact of visual/somatosensory inputs at the single-cell (excitatory neuron
vs GABAergic cells), population and cortical laminar level, in order to better understand the precise nature and
location of crossmodal interactions in both primary and associated sensory areas.
Gentet LJ, Kremer Y, Taniguchi H, Huang ZJ, Staiger JF, Petersen CCH (2012)
Unique functional properties of somatostatin-expressing GABAergic neurons in mouse barrel cortex. Nat Neurosci 15: 607-612.
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Mateo C, Avermann M, Gentet LJ, Zhang F, Deisseroth K, Petersen CCH (2011)
In vivo optogenetic stimulation of neocortical excitatory neurons drives brain state dependent inhibition.
Current Biology, Volume 21, Issue 19, 11 October 2011, Pages 1593–1602
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Gentet LJ, Avermann M, Matyas F, Staiger JF, Petersen CCH (2010)
Membrane potential dynamics of GABAergic neurons in the barrel cortex of behaving mice
Neuron 65: 422-35
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Ferezou I, Haiss F, Gentet LJ, Aronoff R, Weber B, Petersen CCH (2007)
Spatiotemporal dynamics of cortical sensorimotor integration in behaving mice
Neuron 56: 907-23
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This page was last updated on 2 april 2012