Synapse- neurons have firing thresholds and fire when enough ions flow into cell and thresholds are met. Post synaptic response varies according to 3 factors: how much neurotransmitter presynaptic membrane releases- increasing firing rate, sensitivity of postsynaptic cell to neurotransmitters, postsynaptic membranes can receive input from multiple neurons. All or none law: once threshold is met, magnitude of signal produced by axon is always the same, but neuron can fire frequently and for longer periods of time. Cognitive neuroscience techniques: computerized axial tomography (ct/cat scans, computer compares signals from multiple x-ray detectors to pinpoint source of each signal, computer then reconstructs 3d map of brain. Individuals are injected with radioactive substance: photon detectors track radioactive substance in blood, provides measure of glucose levels. Visual system: modality in which humans acquire a lot of knowledge, much is known about neural wiring of visual system.