Computational Approaches to Investigate the Effects of Sensory Stimuli in Brain

Abstract

A fundamental goal of neuroscience is to understand how the brain responds to sensory stimuli. We can employ various computational approaches to solve research problems pertaining to this goal. This thesis, specifically, aims to investigate two such problems using computational approaches.

The first problem deals with the modulation of plantar cutaneous feedback with Transcutaneous Electrical Nerve Stimulation (TENS or E-stim). Plantar cutaneous feedback or tactile feedback from the foot sole is weakened in case of peripheral neuropathy and results in fall-related accidents. Previous studies show E-stim applied on the distal-tibial nerve elicits tactile feedback (Eletrotactile feedback) from heels. We put forward three hypotheses—a) Simple Augmentation Theory, b) Stochastic Resonance Theory, c) Nerve Conduction Block Theory—and used psychophysics to explain how electrotactile feedback modulates plantar tactile feedback. Two experiments involving thirteen healthy participants conclusively proved the validity of the simple augmentation theory that states E-stim augments plantar cutaneous feedback by adding more action potentials. This result suggests that E-stim can be used as a potential treatment for peripheral neuropathy.

The second problem sheds light on the response of auditory and prefrontal cortex to complex acoustic stimuli in echolocating bats. We used two neuroimaging techniques—intrinsic signal imaging and calcium Imaging—to find solutions to this problem. Echolocating bats can decode the shape, size, and texture of an object from echoes, which makes them excellent models to understand more about the sound-processing part of the brain. Since there are no such existing studies on neuroimaging in bats, we conducted a proof-of-concept study for both intrinsic signal imaging and calcium imaging. With the help of intrinsic signal imaging, we showed the existence of tonotopic map in auditory cortex. Furthermore, we transfected the brains of free-tailed bats (Tadarida brasiliensis) with an adeno-associated viral vector (AAV) carrying the gene of GCaMP7s (Calcium Indicator) for calcium imaging. After 6 weeks, we saw a rapid and extensive activity in the medial prefrontal cortex of expressing bats in response to downward frequency modulated sweeps mimicking echolocating calls.