Spreading Activation
   - When neurons fire, they send information down the axons to the
       synaptic cleft, and on to adjacent neurons.
- Earlier simulations had this.
- It increases connection weights
 
- Spread of activation also allows pattern completion effects.
- This in turn allows categorisation, by activating a group of 
       neurons.
- Whichever group is activated is the category with which the
       pattern is associated