Information-theoretic investigation of multi-unit activity properties under different stimulus conditions in mouse primary visual cortex

Primary visual cortex (V1) is the first cortical processing level receiving topographically mapped inputs from the retina, relayed through thalamus. Electrophysiological studies discovered its important role in early sensory processing particularly in edge detection in single cells. To this end, little is investigated how these activities relate on a population level. Orientation tuning in mouse V1 has long been reported as salt-and pepper organised, lacking apparent structure as was found in e.g. cat or primates. This is a novel synthesis of specially designed in-vivo electrophysiological experiments aiming to make certain information-theoretic data analysis approaches viable. Sophisticated state-of-the-art data analysis techniques are applied to answer questions about stimulus information in mouse V1. Multi-unit electrophysiological experiments were devised, performed and evaluated in the anaesthetised and in left hemisphere V1 of the awake behaving, head-fixed mouse. A detailed laboratory and computational analysis is presented validating the use of Multi-Unit-Activity (MUA) and information-theoretic measures. Our results indicate left forward drifting gratings (moving from the temporal to nasal visual field) elicit consistently highest neuronal responses across cortical layers and columns, challenging the common understanding of random organisation. These directional biasses of MUA were also observable on the population level. In addition to individual multi-unit analyses, population responses in terms of binary word distributions appear more similar between spontaneous activity and responses to natural movies than either/both to moving gratings, suggesting that mouse V1 processes natural scenes differently from sinusoidal drifting gratings. Response pattern distributions for different gratings emerge to be spatially but not orientationally clustered. Further computational analysis suggests population firing rates can partially account for these differences. Electrophysiological experiments in the awake behaving mouse indicate V1 to contain information about behavioural outcome in a GO/NOGO task. This, along with other statistical measures is examined with statistical models such as the population tracking model, which suggest that population interactions are required to explain these observations.Open Acces

Temporal encoding, precision, and coordination in a comprehensive, spike-resolved motor program

Animals must execute robust, agile movement in a variety of biomechanical and environmental contexts. The nervous system must encode information for movement across multiple muscles in the "all-or-none" messages of action potentials. Sequences of action potentials, or spikes, can carry information in the number of spikes and their timing. Spike timing codes are critical in many sensory systems, but there is now growing evidence that millisecond-scale changes in timing also carry information in motor brain regions, descending decision-making circuits, and individual motor units. However, a thorough investigation of the importance of spike timing at the millisecond-scale for encoding information, coordinating muscles, and causally changing motor behavior would require recording a comprehensive, spike-resolved motor program across a complete set of muscles that actuate a behavior. This work leverages the comprehensive, spike-resolved motor program of a hawk moth to demonstrate that the currency of motor control is millisecond-scale precise spike timings. In Chapter 2, we show that across the ten muscles that control the wings during flight, spike timing encodes more information about yaw torque than spike rate, and that spike timing encodes all coordinated information between pairs of muscles, despite there being sufficient bandwidth to encode the information in spike rate. In Chapter 3, we introduce a method to assess the necessary spike timing precision to encode information about behavior. In the comprehensive motor program of the hawk moth, the information encoded in spikes is precise to the millisecond or sub-millisecond scale, losing information when noise is added to spikes that exceeds several milliseconds. In Chapter 4, we demonstrate through classification that the motor program we record is indeed comprehensive, capable of near perfect classification of six types of behavior elicited in response to drifting visual stimuli as long as millisecond-scale information about spikes is available. Additionally, we demonstrate consistency in how muscles are coordinated across different types of behavior, though functionally different spiking activity occurs. Finally, in Chapter 5, we investigate specific precise spike timing differences observed in the six behavior types to demonstrate causality of millisecond-scale spike timing for behavior.Ph.D