Figure 2.
Responses to repeated LGN stimulation. A, Top trace, Voltage response of a cortical cell that received monosynaptic input from the LGN to a five impulse, 50 Hz train of electrical stimuli. Bottom trace, Same traces, with slow trends removed as described in Materials and Methods. Average of 16 trials. LGN stimulus amplitude of 200 μA. Resting potential of -60 mV. B, PSPs from A, bottom trace, aligned on the LGN stimulus. The thick trace is the first PSP. C, As in A, for a cell that received only polysynaptic input from the LGN. Average of 16 trials. LGN stimulus amplitude of 225 μA. Resting potential of -71 mV. D, Superimposed responses to individual stimuli, aligned on the LGN stimulus. E, PSP amplitude as a function of stimulus position in the train. Filled symbols, Data for the monosynaptic cell in A and B; open symbols, data for the polysynaptic cell in C and D. Error bars are SE. F, Diagram showing the connectivity of monosynaptic and polysynaptic neurons. Both cell types are thought to receive input from cortical inhibitory interneurons. Monosynaptic cells receive substantial excitatory input from the LGN, whereas polysynaptic cells receive little direct thalamic input and are primarily driven by excitatory input from other cortical cells.