FIGURE 1.

Graded instructive signals in a Purkinje cell. (A) A schematic diagram of a Purkinje cell and its different synaptic inputs. Electrodes are placed in different locations to measure the extracellular spiking activity of the climbing fiber (1; red), a molecular layer interneuron (2; green), a parallel fiber (3; cyan) and the Purkinje cell axon (5; black). In addition, intracellular calcium signals are imaged in one of the Purkinje cell’s distal dendrites (4; black), near electrodes 2 and 3. (B–E) Spikes and calcium signals measured in the five locations shown in (A), under four different scenarios: when all climbing fiber signals are “all-or-nothing” whether firing is spontaneous (spont) or when the strength of stimulation in the inferior olive is weak or strong (B), when instructive signals to lift the foot “a little” or “a lot” influence the number of spikes in the climbing fiber burst (C), or when the instructive signals activate the climbing fiber simultaneously with parallel fiber inputs (D) and input from the molecular layer interneurons (E).