An experiment was conducted to investigate the electrical activity of a postsynaptic neurone, which has a resting membrane potential of -70 mV and a threshold potential of -55 mV. Two separate presynaptic neurones, X X\,X and YYY, synapse with this postsynaptic neurone, as shown in the diagram below:
The table below shows the peak membrane potentials recorded in the postsynaptic neurone under different stimulation conditions:
| Occasion | Presynaptic neurones stimulated | Timing of stimuli | Peak membrane potential of postsynaptic neurone (mV\text{mV}mV) |
|---|---|---|---|
| 1 | X X\,X only | Single stimulus | -62 |
| 2 | Y Y\,Y only | Single stimulus | -62 |
| 3 | X X\,X and YYY | Simultaneous stimuli | +35 |
| 4 | X X\,X only | Two stimuli, 25 ms apart | -62 |
Which of the following, A to D, explains the results in Occasion 3?
Temporal summation
Spatial summation
Inhibitory postsynaptic potentials (IPSPs)
Saltatory conduction