Noema: Hardware-Efficient Template Matching for Neural Population Pattern Detection

Repeating patterns of activity across neurons is thought to be key to understanding how the brain represents, reacts, and learns. Advances in imaging and electrophysiology allow us to observe activities of groups of neurons in real-time, with ever increasing detail. Detecting patterns over these activity streams is an effective means to explore the brain, and to detect memories, decisions, and perceptions in real-time while driving effectors such as robotic arms, or augmenting and repairing brain function. Template matching is a popular algorithm for detecting recurring patterns in neural populations and has primarily been implemented on commodity systems. Unfortunately, template matching is memory intensive and computationally expensive. This has prevented its use in portable applications, such as neuroprosthetics, which are constrained by latency, form-factor, and energy. We present Noema a dedicated template matching hardware accelerator that overcomes these limitations. Noema is designed to overcome the key bottlenecks of existing implementations: binning that converts the incoming bit-serial neuron activity streams into a stream of aggregate counts, memory storage and traffic for the templates and the binned stream, and the extensive use of floating-point arithmetic. The key innovation in Noema is a reformulation of template matching that enables computations to proceed progressively as data is received without binning while generating numerically identical results. This drastically reduces latency when most computations can now use simple, area- and energy efficient bit- and integer-arithmetic units. Furthermore, Noema implements template encoding to greatly reduce template memory storage and traffic. Noema is a hierarchical and scalable design where the bulk of its units are low-cost and can be readily replicated and their frequency can be adjusted to meet a variety of energy, area, and computation constraints.