Excitation: the process by which nerve cells use their “presynaptic terminals” to stimulate the next receiving nerve cell in line to transmit information onward. (Kandel, 71)

The electrical activity in the brain is what tells us that a particular "neuron" has been "activated" at a particular time. It has "fired" as we say, and it has done so in order to “code” either a “sensory” event (example seeing some object or action), a “motor” act (example grasping an apple), or a “cognitive” process (example the memory of grasping an apple). (Iacoboni, 22) The “depolarization” of a “postsynaptic neuron” increasing the likelihood that an "action potential" will be generated. (Kandel, 437) Some neurons function primarily to excite other neurons. (Kolb, 67) "Receptor" activation occurs when a chemical "binds" to a specific membrane protein initiating change. (Norman, 6/10/09) Verb - ‘excite.’ Adverb - ‘excitatory.’ Also referred to as ‘activation,’  ‘stimulation,’ and ‘firing.’ Editor’s note - excitation may apply to a neuron, a “synapse,” a “signal,” a receptor, or a “neurotransmitter.”

Dual Signal: both excitatory and inhibitory. In Dr. Kandel’s research, the same cell excited some follower cells, inhibited others, and made a dual connection (which was both excitatory and inhibitory) to a third kind of cell. It always excited precisely the same cells, always inhibited another specific group of cells, and always made a dual connection with a third group. All of these three actions were accounted for by only one neurotransmitter -  “acetylcholine.” The reaction of acetylcholine with different types of receptors on the various follower cells, determined whether the synaptic action would be excitatory or inhibitory. (The Brain-Eric Kandel, 30)

Excitability Change: the change in the "threshold" (polarity) of a nerve call that follows activity - for example, from positive to negative, or from negative to positive. (Kandel, 437)

Excitatory Interneuron: can be thought of as an ‘amplifier.‘ The output of the (postsynaptic neuron to which it is connected) is amplified. (LeDoux, 53)

Excitatory Neurotransmitter: a signal that excites a neuron. If a neuron receives enough excitatory signals from other neurons, it will fire off its own signal. (Doidge, 54) When excitatory (signals) try to turn on a (postsynaptic neuron), preexisting inhibition of the (postsynaptic neuron) (may) have to be overcome. The balance between excitatory and inhibitory (signals) to a neuron determines whether it will fire. (LeDoux, 51) In the motor neuron, excitatory neurotransmitters lower the “resting membrane potential,” a value, of the post synaptic neuron from -70 millivolts to -55 millivolts. (Therefore) -55 millivolts is the "threshold" for firing an action potential. (Kandel, 98) About 80 percent of the “signaling” in the brain is carried out by two neurotransmitters that balance each other’s effect. The major excitatory neurotransmitter “glutamate” stirs up activity to begin the signaling cascade, and the major “inhibitory" neurotransmitter  “GABA” clamps down on activity. (Ratey, 37) Also referred to as 'excitatory signal.'

Excitatory Receptor: receptor that electively recognizes and "binds" (excitatory) neurotransmitter molecules. (LeDoux, 54) Editor's note - for example, a “glutamate receptor.”

Excitatory Synapse: indicates a synapse that depolarizes its "target," increasing the chance that the neuron will fire. (Kandel, 437)

Firing Rate: the rate at which a cell fires. A function of certain electrical and chemical characteristics of the cell. (LeDoux, 64) Some cells fire action potentials regularly and others fire in recurrent brief bursts or 'trains.' (The Brain-Eric Kandel, 30) Rate varies. Sometimes the rate correlates with clearly definable external factors, like the presence of color in a face. In the “peripheral nervous system” more spikes mean more heat, a louder sound, or stronger (faster) muscle contraction. (Discover, Aug 2007, 56)

Single Neuron Insufficiency Principle: a single neuron individual firing rate is insufficient to sustain a particular function or behavior mediated by the cortex. (Nicolelis, 168) The arrival of transmitter from a single presynaptic terminal is typically not sufficient to produce an action potential in the postsynaptic cell. Only if the postsynaptic cell is bombarded with transmitter molecules from many presynaptic terminals at about the same time - within milliseconds- will an action potential results. (LeDoux, 47)

Tonically Active: (neurons that) are firing all the time. (LeDoux, 50)