Visual cortical neurons
Sensory neurons encode information about stimuli in the timing, and rate, of action potentials. Neurons in different areas of the brain are sensitive to different stimulus properties. For example, in primary visual cortex (V1), neuronal responses are strongly affected by the orientation of a stimulus. For a single neuron, different orientations evoke different rates of spiking; and different neurons have different "preferred" orientations. The video on the right shows recordings made in the 1960s from the laboratory of David Hubel and Torsten Wiesel, who first demonstrated orientation selectivity in V1, and won a Nobel prize for related work on the visual system. You can hear the amplified ‘spiking' activity of a single cortical neuron, and see the visual stimulus that has evoked that activity. As you watch the video, think about the properties of the stimulus that evokes the weakest and strongest neuronal responses.
In the middle temporal area (MT), neuronal responses are strongly affected by orientation, but also by the direction and speed of moving objects. While each direction evokes a different average spiking rate, the responses to repetitions of the same stimulus are surprisingly variable. A further complication is that responses scale with contrast – larger responses are seen at higher contrasts.
This means that given the spiking responses of just one neuron, it is impossible to determine what stimulus was presented. For example, a spiking rate of 30 spikes in a second might be evoked by a fast, high contrast stimulus moving upwards, or a slow, low contrast stimulus moving to the right. The brain therefore relies on populations of neurons to reliably encode stimulus features.
In this simulation, you will quantify how the responses of a typical neuron in MT depend on motion direction, contrast, and some other unrevealed factors. This can be used to assess how much information a neuron conveys about the stimulus, and the reliability of that information. We can then infer how populations of neurons work together to accurately encode a diverse range of stimuli.