The neural mechanisms that lead to sparse coding within the midbrain of weakly electric fish

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As you are reading this text, neurons in your brain allow you to distinguish the various letters forming words and sentences, thereby forming a neural representation that changes from brain area to brain area. While neurons in more peripheral areas (e.g., your retina) tend to respond to the physical attributes of the sensory input (e.g., the luminance and contrast of the image), neurons in more central brain areas (e.g., your visual cortices) instead tend to respond more to abstract features (e.g., the letter "d" but not the letter "b"), despite obvious similarities (e.g., one is the mirror image of the other). This is known as "response selectivity" and has been observed across systems (visual, auditory, somatosensory, olfactory) and species ranging from insects to us. At the same time, neurons in more central brain areas become more tolerant to identity preserving transformations of sensory input (e.g., a neuron would respond to the letter "d" irrespective of size or font). This is known as invariance and has also been observed across systems and species. Perhaps the best-known example of invariance is the so-called "Jennifer Anniston" neuron that respond to pictures of the actress irrespective of viewpoint but not of another person (e.g., Halle Berry). There thus needs to be a balance between selectivity, which aims at restricting the stimuli that give rise to neural responses and invariance, which instead aims at expanding the stimuli that give rise to neural responses. Such a balance is absolutely essential in order for us to recognize other people and objects in our environment, thereby allowing us to successfully interact with our environment. However, the mechanisms that lead to selectivity and invariance are poorly understood in general in vertebrates, and even less is known about how a balance between both is achieved. Here I propose to study these using a combination of neural recordings and behavioral approaches using the electrosensory system of weakly electric fish. This model system shares many similarities with our auditory and visual systems and has the advantage of well-characterized anatomy and circuitry. Moreover, sensory stimuli can easily be mimicked in the laboratory and will give rise to reliable behavioral responses. Using new technology that allows us to record from large neural ensembles, we will be able to understand how network (i.e., how neural circuits are organized in the brain) versus intrinsic (i.e., how various components of the single neuron) interact to achieve a tradeoff between selectivity and invariance. The results of this research are expected to further our understanding of basic brain function and could potentially be used to understand how the tradeoff between selectivity and invariance is achieved in higher vertebrates.