Some of the most important developments in brain-computer interfacing have come from BCIs based on invasive recordings. As reviewed in Chapter 3, invasive recording techniques allow the activities of single neurons or populations of neurons to be recorded. This chapter describes some of the achievements of invasive BCIs in animals and humans.

Two Major Paradigms in Invasive Brain- Computer Interfacing

BCIs Based on Operant Conditioning

A number of BCIs in animals have been based on operant conditioning, a phenomenon discussed in Section 6.2.1. In operant conditioning, an animal receives a reward upon selection of an appropriate action, e.g., pressing a lever. After repetitive pairing, the animal learns to execute the action in anticipation of the reward. In a BCI paradigm, the animal is rewarded if it selectively activates a neuron or population of neurons to move a cursor or prosthetic device in an appropriate manner.

Early BCI Studies

In the late 1960s, in one of the earliest demonstrations of brain- computer interfacing, Eberhard Fetz at the University of Washington in Seattle utilized the idea of operant conditioning to demonstrate that the activity of a single neuron in a primate’s motor cortex can be conditioned to control the needle of an analog meter (Fetz, 1969). The movement of the needle was directly coupled to the firing rate of the neuron: when the needle crossed a threshold, the monkey was rewarded. After several trials, the monkey learned to consistently move the needle past the threshold by increasing the firing rate of the recorded neuron (Figure 7.1). In this example of operant conditioning, the action (needle movement) that produces reward is coupled to increased activity in the recorded neuron (the conditioned response).