Why study learning and memory formation?

This is pretty obvious: our thoughts and memories makes us who we are, without remembering we loose our personality.

“Tell me where dwell the thoughts, forgotten till thou call them forth?
Tell me where dwell the joys of old, and where the ancient loves,
And when will they renew again, and the night of oblivion past,
That I might traverse times and spaces far remote, and bring
Comforts into a present sorrow and a night of pain?
Where goest thou, O thought? To what remote land is thy flight?
If thou returnest to the present moment of affliction,
Wilt thou bring comforts on thy wings, and dews and honey and balm,
Or poison from the desert wilds, from the eyes of the envier?”

                                                            (William Blake 1793 Vision of the daughters of Albion)   

Why study learning and memory in a snail?

Just like vertebrates, molluscs can also be trained by using classical Pavlovian conditioning paradigms. In most training paradigms used in the common pond snail (Lymnaea stagnalis), long-term memory (LTM) forms after multiple-trials, but LTM can also form after certain types of single-trial conditioning.

The major advantage of using the relatively simple nervous system of Lymnaea is that unlike in the complex mammalian brain the neurons are well identified and the neuronal circuits thoroughly described. The large (up to 150µm) brightly coloured neurons are easily accessible; by inserting microelectrodes into the cells the electrical activities of identified neurons can be recorded. Molecular changes induced by learning can be measured in parts of the brain and also in individual cells. Since all these fundamental processes are evolutionary highly conserved our results provide a high resolution insight into mechanisms of memory formation that would not be possible to study in the complexity of the vertebrate nervous systems.

What are the goals of our research?

We have been studying learning and memory related mechanism for over 20 years in Sussex. Our recent research focuses on two major areas, decision making and lapses in memory formation.

1. How can learning influence decision making?

 A key function of even the simplest nervous systems is to decide which behavior to initiate next in a world where organisms are bombarded by a whole variety of sensory stimuli. To understand how such decision making is carried out we need neuron-by-neuron analysis of networks that are engaged in specific instances of behavioral decision making. In Lymnaea we used two mutually exclusive neuronal circuits, feeding and withdrawal to study the mechanism of decision making. The single trial associative Pavlovian conditioning paradigm is used to study how learning can modify decision making.

2. How can lapses during consolidation alter the fate of memory?

Lapses are brief periods during the early phases of memory formation when memory recall is weakened or absent. The existence of such lapses can be interpreted as maladaptive because they interrupt the process of memory formation. Our recent work on the snail Lymnaea however suggests that they are adaptive, allowing consolidation to be regulated so that acquisition and storage are effectively modified by new information after initial learning.It is a phenomenon that would be very difficult, if not impossible to examine in the complex human brain. However the Lymnaea model system is well suited for the exploration of this fundamental issue in the formation of new memories.