Encoding of Interval Time within the Rat Hindlimb Sensorimotor Cortex
Authors:   , Knudsen Eric Bean , Wheatley Margaret A. 
Published: July 2021

Temporal intervals, on the order of seconds to minutes, have been shown to be encoded by neurons in several brain regions including the forelimb representation in primary motor cortex (Lebedev et al. 2008; Roux et al. 2003). Many studies have demonstrated encoding of temporal intervals by single neurons through a 'scaling' of the average rate of change of the firing rate of the cell proportional to the length of an interval (slope scaled). Essentially, for two given intervals, a neuron will reach a conserved peak discharge at a rate scaled to the length of the interval. This information could prove useful in decoding temporal sequences of movements in a brain-machine interface (BMI) paradigm, however it is unclear if this type of activity occurs in the absence of timed movements and after spinal cord injury. The long term goal motivating this doctoral thesis is to be able to decode temporal intervals on a single trial basis for use in a brain-machine interface that controls the temporal sequence of hindlimb movements after spinal cord injury. The goal of this project is to understand the encoding of temporal intervals on a single trial basis (1) during hindlimb movements, (2) during a BMI paradigm in the absence of movement and (3) after a complete spinal transection. The project's central hypothesis is that the temporal context which defines the behavioral relevancy of the interval is necessary for temporal scaling but temporal scaling is not dependent on the part of body used in the task (AIM I), whether any part of the body moves in response to encoding (AIM II) or whether the brain is still connected to that part of the body (AIM III). This central hypothesis is addressed by three Specific Aims: Specific AIM I: Identify the role of temporal context (i.e. relevancy of press interval) in the encoding of temporal intervals in the hindlimb motor cortex (HLSMC) when rats plan and perform a skilled hindlimb movement. Hypothesis: Despite the fact that animals can make presses of varying intervals under different temporal contexts, neurons within HLSMC will encode interval time through patterns of temporally scaled activity only when the temporal interval is behaviorally relevant (i.e. the animal is rewarded for a specific interval). AIM Ia: Determine if neurons within the infragranular layers of rat hindlimb sensorimotor cortex (HLSMC) utilize temporal scaling to encode for temporal intervals AIM Ib: Determine if the temporal scaling is required for producing presses of varying intervals. Specific AIM II: To investigate the effects of a brain-machine interface on the encoding of temporal intervals Hypothesis: Neurons will continue to use temporal scaling to encode for abstracted temporal intervals, despite no longer explicitly timing behavioral movements. Specific AIM III: Identify the impact of a complete spinal cord transection on the encoding of temporal intervals. Hypothesis: Despite complete disconnect of HLSMC circuitry from the periphery, HLSMC neurons will continue to encode abstracted temporal intervals through temporally scaled patterns of activity.