Tactile discrimination learning in mice

In order to investigate neuronal activity associated with learning, it is important to use robust behavioural tests that are rapidly acquired, long-lasting and reliant on the sensory modality under investigation. Chapter 1 provides an overview of the whisker-barrel system and currently available behavioural tasks used to assess texture-based learning in mice. A selective review is then presented which highlights the current understanding of synaptic plasticity in the barrel cortex. Chapter 2 reports the findings of a modified novel object recognition task that uses 3-D printed stimuli to assess texture recognition memory. The experiments revealed that mice can retain a memory of tactile stimuli across a 24-hour period, however, the procedure required a large number of animals. Chapter 3 describes the development of a texture-based two-choice discrimination task. The experiments demonstrated that mice can learn rapidly a texture-based discrimination and remember the discrimination over a 24-hour interval. The experiments also revealed that discrimination learning is whisker-dependent: whisker trimming impaired the animals’ ability to learn the texture-discrimination but had no effect on an odour-discrimination. Chapter 4 explored the role of the barrel cortex in the new texture discrimination procedure by reducing the activity of neurons in layer 4 of the barrel cortex using the chemogenetic DREADD technology. The results revealed that reducing activity of these neurons resulted in an inability to acquire the texture discrimination, but did not impair performance on an equivalent odour discrimination task. Analysis of cFos levels, as a proxy for neuronal activity, revealed that in cases infected with DREADDs and activated by CNO, cFos levels were increased in PV cells and decreased in non-PV cells. Together, these experiments suggest a critical role for the barrel cortex in whisker-dependent texture discrimination learning. Chapter 5 explores the broader implications of these results and makes recommendations for future experiments investigating the neural basis of texture discrimination