Let’s Get V1sual! V1sual!

When I first sat down with Lindsey Glickfeld, she explained every unknown neurobiology term with a diagram, which I will try to emulate throughout this blog post. I think trying to explain the Glickfeld Lab’s focus on the synaptic organization of the mouse visual cortex with words might be a bit tiring on the eyes. I want to give a little background on the mouse visual cortex since the Glickfeld Lab uses the mouse model; I hope the diagram and its caption below is more appealing than a big blob of words!

(A) Follow the right side of the flow chart . . . Visual processing begins in retina, then to the dorsal lateral geniculate nucleus (dLGN) in the thalamus. From dLGN, the visual information moves to the primary visual cortex (V1) and then to the higher visual areas (HVAs). (B) A zoomed in diagram of V1 and different HVAs. Please ignore the red . . . most of this blog’s focus is on V1 to LM, AM, and PM.

Before I dive a little deeper into my project, I want to define some neurobiology jargon that is essential to understand this research at the Glickfeld Lab. Surround suppression can be defined as the “neuron’s initial increase in firing is followed by a decrease in firing as the stimulus become progressively larger,” and visual receptive fields can be defined as “a portion of sensory space that can elicit neuronal responses when stimulated.” But, maybe this diagram of surround suppression on one specific neuron might make a little more sense; the receptive field is drawn as the red and green figures and the stimulus as the white and black gratings.

Surround suppression is shown through the initial direct relationship between firing rate and stimulus size following an inverse relationship between the same variables.

Now that the background is out of the way, I’ll start to explain what I plan to research this summer. I am working under Jenny Li, my mentor, who is focused on the pathway from the primary visual cortex (V1) to higher visual areas (HVAs). Past research has looked at V1 and three HVAs that receive the strongest direct input from V1: lateromedial (LM), anterolateral (AM), and posteromedial (PM). However, there was one HVA that caught researchers’ eyes: PM. Unlike the other two HVAs, PM had significantly less surround suppression and bigger receptive fields (see below for yet another diagram!). Jenny is interested in these differences between higher visual areas.

To discover and eliminate variables that may play into this phenomenon, I will be measuring the width of axon spread from V1 to HVAs. I will accomplish this by performing burr hole surgeries for viral injections, perfusions, brain slicing, and finally imaging. If there are differing widths of axon spread, it could be a possible anatomical explanation for why PM show less surround suppression and larger receptive fields than other prominent HVAs.

In the bigger picture, the mouse’s visual system is different from the primate’s  visual system: lower acuity, lack of trichromacy and fovea, and more. However, the similarities do outnumber the differences. Furthermore, it is much easier to monitor and manipulate specific cells types and circuits in mice, helping us advance towards to goal of understanding how vision works. By studying the mouse’s cortical circuits rather than its vision, researchers can discover fundamental principles of cortical processing that may be universal across species. 

Some coronal brain slices!

Mounted coronal slices!

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