Activation of the neuron

The neurons in both the hidden and output layers perform summing and nonlinear mapping functions. The functions carried out by each neuron are illustrated in Fig. 2. Each neuron occupies a particular position in a feed-forward network and accepts inputs only from the neurons in the preceding layer and sends its outputs to other neurons in the succeeding layer. The inputs from other nodes are first weighted and then summed. This summing of the weighted inputs is carried out by a processor within the neuron. The sum that is obtained is called the activation of the neuron. Each activated neu-... 

D-amphetamine stimulates the release of monoamines independently of the electrical activity of the neuron. This release leads to an increased concentration of monoamines in the synaptic cleft and, thus, an increase in receptor stimulation. Drugs, such as amphetamine, that do not bind to receptors, but increase the availability of the neurotransmitter by stimulating its release or inhibiting its inactivation, are called indirect agonists. 

Interference with the transmembrane flux of Na+ and K+ ions and, thus, the electrophysiological activity of the neuron. 

Weit Most people would assume that for secreted factors, even those acting at a distance in paracrine fashion, release is likely to be gated by electrical activity of the neuron. Most likely electrical activity of SCN neurons is important for the release of conventional synaptic factors or hypothetical paracrine factors. 

The model represents learning in terms of the well known Hebb s hypothesis [10]. According to it learning manifests itself in the modification of synaptic connections between all i s and j s as a new object (a pattern of +1 and —1) comes to be recorded. The effectiveness or the strength of a synapse - whether it is excitatory (i.e. Jy > 0) or inhibitory (i.e. Jy < 0) - is believed to be altered by the activities of the neurons it connects. This flexibility of the synapses is modelled in the following choice of J,... 

Secretion of oxytocin is regulated by the electrical activity of the neurons in the hypothalamus, which generate action potentials that propagate down axons to the nerve endings in the pituitary. These axons contain oxytocin-containing vesicles, which are released when the nerve terminals are depolarized. 

The cholinergic system in insects is the main target of insecticides. One class of molecules, the neonicotinoids, induces direct activation of the neuronal nicotinic acetylcholine receptors (nAChRs). In the honey bee these receptors are mainly distributed in the olfactory pathways that link sensory neurons to antennal lobes and mushroom bodies. These structures seem to play an important role in olfactory conditioning. We have previously shown that cholinergic antagonists injected in different parts of the brain impaired the formation and retrieval of olfactory memory. We then advanced the hypothesis that, through the activation of the nAChR, the neonicotinoid imidacloprid (IMI) would lead to facilitation of the memory trace. 

Usually, in cases of process modeling, this threshold is replaced by an activation function, making the activation of the neuron continuously valued. However this function has to be differentiable, and it has to saturate at both ends. When the neuron fires, this means that its output H has a value different than zero. The type of network that is used will determine the actual value of H. Sometimes H is simply one (a binaiy network), for other networks H is... 

The third approach is Hebbian learning, where learning is done locally by adjusting the weight based on the activities of the neurons. 

---