But what does science tells you about learning and memory? How does this fit with PBL? Interested connections appear as the scientists find out more about how the brain in general works. It is common knowledge nowadays that memory does not be found in a single molecule or even in a group of nerve cells. This is a very oldfashioned and clumsy way to look at storing memory; like memory were stored in small "boxes" in the brain, ready to pick out whenever you want to. It doesn't work like that. Memorising things is an active and creating process, which occurs in the brain during several steps and for rather a long time. The memory is also located everywhere in the brain, and its not connected to some separate molecule or even a group of neural cells. Memory seems to be organised like a labyrinth, rather than a cerebral warehouse filled with rows and rows of neatly ordered filing cabinets. It behaves more like an intricate and ever-shifting net of firing neurones and crackling synapses distributed throughout the brain. Some professor from Open University in Milton Keynes called Steven Rose, did make a lot of experiments with chickens. He came to the conclusion that learning initiates a cascade of proteinsyntesis and neural bursting activity in the brain. He identified two distinct stages through which an experience must pass before it enters long time memory (LTM). Other scientists have discovered similar memory mechanisms in other species. The formation of short time memory (STM) takes place 15 to 30 minutes after a chick is trained. But it is unstable an easy to disrupt. During this stage, cerebral cortex is flooded with glutamate, the primary information carrier both in chick and human brains. It opens the communication channels between neurones so that data about the experience - encoded in electrical and biochemical signals - can be transmitted through the synapses, the crucial first step in making memories. Glutamate is intimately involved in early phase of memory formation. By chemically block the glutamate receptors out chickens were unable to recall the experience a few ours later. The formation of LTM memories requires a second wave that takes place some five or eight hours after training. A special production of a class of proteins known as cell adhesion molecules is intimately locked to this stage. They have "sticky" ends, which enables them to cling to the "sticky" ends of their partner molecules. When they latch on to one another, the arrangements of synapses in the chick brain changes. The skein of synaptic connection shifts as the training becomes embedded in the brain. The memory of the new experience is caught in the synaptic lattice.

 In neurobiological terms, this protein of synaptic change is the memory itself. A couple of professors in other universities have noticed that neurones in hippocampus, a campusformed region in the brain, closely linked to short time memory the scientists described "synaptic tags" that capture protein messenger at key junctions in the neural net. By anchoring proteins to the synapse these molecular tags boost the synapse's ability to send and receive impulses. This process probably results in the construction of markers for distinct neural patterns. Thus when an experience alters the connections along a specific alignment of synapses the new markers could note the configuration like a set of biochemical bookmarks. When the event is subsequently recalled, brain could use this markers as handy reference points for recreating the neural firing pattern of the original experience.