cognitive and systems neuroscience group Pennartz lab
Background research project
Early perspectives on information processing by the brain’s visual system suggest that it is comprised of separate information streams, each specialized in predominantly processing distinct visual features, like motion or shape (Felleman & Van Essen, 1991; Zeki, 1978; Livingstone & Hubel, 1988). These specialized streams are thought to emerge in the primary visual cortex, where neurons carry out a local analysis of the information present within their small receptive fields and subsequently project this information towards higher visual areas (HVAs) in a feedforward and hierarchical manner (Coogan & Burkhalter, 1993; Johnson & Burkhalter, 1997). Here, neurons have much larger receptive fields than V1 neurons (Desimone & Duncan, 1995), indicating that HVA neurons receive and combine information from multiple V1 neurons (Meijer et al., 2020). Therefore, at higher levels of visual processing, HVA neurons represent the visual scene more globally and are known to be involved in object identification, segmentation, separation and categorization (Lewis et al., 2004; Nayar et al., 2015; Neiworth, Gleichman, Olinick, & Lamp, 2006). However, when processing ambiguous scenes (e.g., occluded or incomplete objects) the local analysis by lower levels reaching the HVAs might be insufficient, suggesting that the brain should incorporate an integrative process to generate the global image we perceive.
One way to examine the brain’s ability to process incomplete objects, is by using illusory contour stimuli such as Kanizsa figures. Here, the local image elements (i.e., the pacman inducers) are arranged in such a way that a global illusory-contour figure can be perceived, which appears to have clear object boundaries as well as a brighter inner region compared to the background (see the figure above; Conci et al., 2007). Although illusory contour processing has been extensively examined in a variety of species, including humans (Conci et al., 2007; Altschuler et al., 2012), non-human primates (Pan et al., 2012; Fagot et al., 2001) and cats (Bravo et al., 1988; Weerd et al., 1990), much less is known on illusory contour processing in rodent species. Recent advances, however, have shown that mice too are able to perceive illusory contours when presented with illusory bar-like stimuli (Pak et al., 2018; Okuyama-Uchimura & Komai, 2016). Even more important, mouse V1 neurons respond similarly to illusory borders compared to cat and primate V1 neurons, and optogenetic silencing of LM (mouse equivalent of primate V2) strongly suppressed V1 responses to illusory contour borders. Together these findings suggest that mice can perceive illusory contour borders, and that top-down Lilian Emming firstname.lastname@example.org
connections from HVAs are responsible for the illusory border processing in V1 neurons (Pak et al., 2019).
This study aims to further elaborate the existing body of illusory-contour processing literature by addressing how local versus global illusory-contour image elements are represented by V1 and its neighbouring HVAs during wakefulness and anaesthesia. Using a combination of calcium-imaging data- and decoding analyses, we specifically aim to disentangle what information is represented by single versus populations of neurons across the visual hierarchy of mice (e.g., areas V1, LM, AL, RL, AM, PM). By combining these approaches, we will additionally develop representational measures of consciousness.
The students role in this project
In the coming months, we will focus on developing widefield and two-photon calcium imaging protocols for animals passively observing illusory contour stimuli. This involves 1) viral injection surgeries to infect neurons in our target areas with viral particles so that fluorescence can come to expression 2) Imaging of GCaMP expression using a combination of widefield and two-photon imaging techniques 3) develop and test protocols for retinotopic and receptive field mapping using intrinsic signal imaging and two-photon imaging and 4) Training mice on a 2-AFC task.
We are looking for an ambitious student that will be responsible for daily behavioural training, assists during a variety of surgeries (i.e., head bar and cranial window implantation, viral injection surgery), performs histology to examine GCaMP6f expression in post-mortem brain tissues using fluorescence microscopy, and will analyse preliminary two-photon imaging and behavioural data in MATLAB and/or Python.
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