Voltage-sensitive dye imaging of mouse neocortex during a whisker detection task

Sensorimotor processing occurs in a highly distributed manner in the mammalian neocortex. The spatiotemporal dynamics of electrical activity in the dorsal mouse neocortex can be imaged using voltage-sensitive dyes (VSDs) with near-millisecond temporal resolution and similar to 100-mu m spatial resolution. Here, we trained mice to lick a water reward spout after a 1-ms deflection of the C2 whisker, and we imaged cortical dynamics during task execution with VSD RH1691. Responses to whisker deflection were highly dynamic and spatially highly distributed, exhibiting high variability from trial to trial in amplitude and spatiotemporal dynamics. We differentiated trials based on licking and whisking behavior. Hit trials, in which the mouse licked after the whisker stimulus, were accompanied by overall greater depolarization compared to miss trials, with the strongest hit versus miss differences being found in frontal cortex. Prestimulus whisking decreased behavioral performance by increasing the fraction of miss trials, and these miss trials had attenuated cortical sensorimotor responses. Our data suggest that the spatiotemporal dynamics of depolarization in mouse sensorimotor cortex evoked by a single brief whisker deflection are subject to important behavioral modulation during the execution of a simple, learned, goal-directed sensorimotor transformation. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

Parallel pathways from whisker and visual sensory cortices to distinct frontal regions of mouse neocortex

Alexandros Kyriakatos, Céline Matéo, Carl Petersen, Varun Sreenivasan

The spatial organization of mouse frontal cortex is poorly understood. Here, we used voltage-sensitive dye to image electrical activity in the dorsal cortex of awake head-restrained mice. Whisker-deflection evoked the earliest sensory response in a localized region of primary somatosensory cortex and visual stimulation evoked the earliest responses in a localized region of primary visual cortex. Over the next milliseconds, the initial sensory response spread within the respective primary sensory cortex and into the surrounding higher order sensory cortices. In addition, secondary hotspots in the frontal cortex were evoked by whisker and visual stimulation, with the frontal hotspot for whisker deflection being more anterior and lateral compared to the frontal hotspot evoked by visual stimulation. Investigating axonal projections, we found that the somatosensory whisker cortex and the visual cortex directly innervated frontal cortex, with visual cortex axons innervating a region medial and posterior to the innervation from somatosensory cortex, consistent with the location of sensory responses in frontal cortex. In turn, the axonal outputs of these two frontal cortical areas innervate distinct regions of striatum, superior colliculus, and brainstem. Sensory input, therefore, appears to map onto modality-specific regions of frontal cortex, perhaps participating in distinct sensorimotor transformations, and directing distinct motor outputs. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

SPIE-Intl Soc Optical Eng2017

Two-photon calcium imaging of neocortical projection neurons in whisker somatosensory cortex during goal-directed sensorimotor learning

Dimitra Angeliki Vavladeli

Abstract Excitatory projection neurons of the neocortex are thought to play important roles in per-ceptual and cognitive functions of the brain by directly connecting diverse cortical and subcortical areas. However, many aspects of the anatomical and functional organization of these inter-areal connections are unknown. The mouse primary somatosensory whisk-er barrel cortex (S1) serves as an important model for investigating the mammalian neo-cortex, and, here, I firstly investigate the structure and secondly the function of a specific subset of S1 cortico-cortical long-range projection neurons. In the first part of my thesis, I studied long-range axonal projections of excitatory layer 2/3 neurons with cell bodies located in S1. As a population, these neurons densely projected to secondary whisker somatosensory cortex (S2) and primary/secondary whisker motor cortex (M1/2), with additional axon in the dysgranular zone surrounding the barrel field, perirhinal temporal association cortex and striatum. The execution of a goal-directed behavior requires the brain to process incoming sensory information from the environment in a context-, learning- and motivation-dependent manner in order to perform specific motor actions. Cortico-cortical communica-tion in the context of goal-directed sensorimotor transformation has begun to be studied, but little is known about how signaling between interconnected cortical areas is modified by sensorimotor learning, as well as in response to changes in reward contingencies. Hence, in the second part of my thesis, I studied cortico-cortical dynamics in primary whisker somatosensory barrel cortex (S1) of mice during a combined whisker and audito-ry task. Using transgenic mice expressing GCaMP6f combined with two-photon micros-copy and retrograde labeling techniques, I chronically monitored the activity of excitatory layer 2/3 neurons in S1 projecting to M1 or S2, while mice learned the behavioral switch task. The results demonstrated that both classes of neurons responded after whisker and auditory stimulation. However, the whisker stimulus evoked response was stronger than the auditory stimulus evoked response. Neurons projecting to S2 exhibited stronger re-sponses compared to neurons projecting to M1 neurons. Those responses remained rela-tively stable across training sessions and under different reward conditions. Furthermore, both classes of neurons responded during spontaneous licking, but neurons projecting to S2 had larger licking-related responses compared to neurons projecting to M1. This work therefore furthers our knowledge of the structure and function of specific types of cortical projection neurons, which is a necessary step towards detailed under-standing of how sensory information might be signaled from primary sensory areas to downstream brain regions for further processing.

EPFL2018

Two-photon calcium imaging of neocortical projection neurons in whisker somatosensory cortex during goal-directed sensorimotor learning

Dimitra Angeliki Vavladeli

EPFL2018