MacRetina simulates an experiment in which students record data from retinal ganglion cells, the cells in the retina that send information from the eye to the brain. By sampling neural activity while stimulating with small spots of light, students can see the dynamic excitatory and inhibitory responses of these neurons, and map the organization of the retinal region that drives each cell (the cellís receptive field). MacRetina is modeled accurately on published data and is a realistic simulation of a lab experiment that would otherwise be beyond the reach of undergraduates.
The program models 10 retinal ganglion cells with overlapping receptive fields. A cell may be an on-center type cell or an off-center type cell and may have either sustained or transient response dynamics. In the figure below the gray region represents a tiny area of retina, 0.5 x 1.0 mm in size. The user maps the excitatiory region of the cell by sweeping the cursor, which represents either a light or dark stimulus projected onto the eye of a cat, across the retinal area.
When the stimulus spot (the cursor) is in the excitatory part of the cell's receptive field, the cell will fire at a high rate. In an experiment, moving the spot in the retinal area will leave a dot at the spot's location each time the cell fires a spike. Action potentials that are picked up from the ganglion cell appear as vertical lines (spikes) on the oscilloscope, displayed above the retinal region, and are heard as clicks. Students learn to recognize the activity patterns of on-center and off-center ganglion cells and how to distinguish between sustained and transient responses. By mapping several different cells with overlapping receptive fields, they can evaluate the way the visual image is analyzed simultaneously by many neurons acting in parallel.
Students can save and print their maps. Several students can map the same set of cells and then compare their results to see if their work is consistent with what others find.
Version 1 of MacRetina received a "Distinguished Natural Sciences Software" Award in 1992 from EDUCOM. Version 2 adds new features that were widely requested by users of Version 1.
Macintosh or Power Macintosh