• Superior colliculus participation in rat vibrissa sensorimotor loops

      Hemelt, Marie E.; Keller, Asaf (2009)
      The neural computations taking sensory input from the periphery and converting it into relevant, meaningful information about the environment perform a complex task. The nervous system must also use this extracted information to create appropriate motor responses to interact with the environment. This dissertation investigates both sensory and motor processing that occur in the rat vibrissa (whisker) model. In particular, I focus on the superior colliculus, which I show both processes sensory information and contributes to vibrissa movement. Electrophysiological recordings in the superior colliculus reveal neurons that respond to vibrissa deflection with large magnitudes and short latencies, consistent with being driven by inputs from the interpolaris nucleus of the trigeminal complex (SpVi). These characteristics, compared to other regions in the vibrissa pathway, seem well suited for the likely role of the colliculus in orienting and attentive behaviors. These neurons have very large receptive fields and high angular selectivity, leading to the question of whether this selectivity is conserved across the receptive field. While neurons in the colliculus have low angular consistency across the receptive field, it is higher than that found in the ventral posteromedial nucleus of the thalamus or the barrel cortex, and similar to that found in the second somatosensory cortex. This is likely a result of inputs to both the colliculus and the second somatosensory cortex from SpVi. Electrical stimulation in the colliculus produces large, multi-vibrissa movements, which persist after motor cortex lesion, and occur with very different kinematics from those produced in the motor cortex. Recordings from tecto-facial neurons reveal that these neurons do not respond to any sensory input, including vibrissa deflection, at least in the anesthetized preparation. Recordings of local field potentials reveal that areas of the colliculus that project to facial neurons do not appear to overlap with areas receiving direct somatosensory inputs from the vibrissae. While I show vibrissa-responsive neurons projecting to premotor neurons in the facial nucleus are not exhibiting suprathreshold responses in the anesthetized rat, intrinsic connections are known to exist in these regions of the colliculus, and these are likely to facilitate sensory influence on vibrissa motor outputs.