A more up to date conclusion for the lectures on classical conditioning is to differentiate between the molecular question of memory, which asks how individual neurons and indeed individual synapses change in order to establish conditioned responses in simple animals such Aplysia, and the “systems question of memory”, which applies to how different parts of the vertebrate brain work to in the formation of different sortsof Pavlovian associations. One reference for this is Kandel and Pittenger (1999). The abstract and some brief relevant extracts from this are given below.

Another relevant reference used in the lectures was Cardinal et al., (2002), who said “Pavlovian conditioning is not a unitary process”, since it can involve both stimulus-stimulus and stimulus-response associations, as well as associations between the conditioned stimulus and emotional states or arousal.  


Kandel, E. R., & Pittenger, C. (1999). The past, the future and the biology of memory storage. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 354(1392), 2027- 2052.

We here briefly review a century of accomplishments in studying memory storage and delineate the two major questions that have dominated thinking in this area: the systems question of memory, which concerns where in the brain storage occurs; and the molecular question of memory, which concerns the mechanisms whereby memories are stored and maintained. We go on to consider the themes that memory research may be able to address in the 21st century Finally, we reflect on the clinical and societal import of our increasing understanding of the mechanisms of memory, discussing possible therapeutic approaches to diseases that manifest with disruptions of learning and possible ethical implications of the ability which is on the horizon, to ameliorate or even enhance human memory.




The work of Ramon y Cajal at the beginning of the century (Cajal 1893) and of Donald Hebb in 1949 (Hebb 1949) established a useful conceptual framework for the study of memory, based on the idea that memory is stored as changes in the strength of specific synaptic connections. This framework divides the study of memory into two components: the systems problem and the molecular problem. The systems problem of memory is concerned with where in the brain memory is stored and how neural circuits work together to create, process and recall memories. The molecular problem of memory is concerned with the mechanisms whereby synapses change and information is stored. Most early work on memory focused on the systems problem, focusing on the question ‘Where is memory stored?’ (pp. 2027-8


We have at this point a clearer understanding of biologically meaningful subdivisions of memory storage and clearer understanding in outline of some molecular mechanisms of storage relevant to each of these subdivisions. Most impressive is the finding that explicit and implicit storage seems to use a common and limited set of mechanisms to convert short- to long-term memory.

Whereas satisfactory insight into even the details of the storage mechanisms are in sight, the systems problems are much more difficult and will continue to occupy us for many decades. This is because the anatomical system that stores explicit memory is complex, as is the nature of the memory that is stored. Moreover, explicit memory is intimately joined with conscious recollection, an area of neuroscience into which we have little insight. Because the complexity of explicit memory will take time to dissect (probably another century) it will be advisable to continue to analyse instances of implicit memory storage, including the simple implicit memory systems of vertebrates and invertebrates, and use them as prototypes for understanding more complex explicit systems. Because explicit memory storage is so deeply embedded in perception, action and consciousness, its future is the future of neuroscience. (pp. 2048).




Clark, R. E., Manns, J. R., & Squire, L. R. (2002). Classical conditioning, awareness, and brain systems. Trends in Cognitive Sciences, 6(12), 524-531. normal gif version of this paper (log on first for for access outside the College)

Memory is composed of several different abilities that are supported by different brain systems. The distinction between declarative (conscious) and nondeclarative (non-conscious) memory has proved useful in understanding the nature of eyeblink classical conditioning -the best understood example of classical conditioning in vertebrates. In delay conditioning, the standard procedure, conditioning depends on the cerebellum and brainstem and is intact in amnesia. Trace conditioning, a variant of the standard procedure, depends additionally on the hippocampus and neocortex and is impaired in amnesia. Recent studies have sharpened the contrast between delay and trace conditioning by exploring the importance of awareness. We discuss these new findings in relation to the brain systems supporting eyeblink conditioning and suggest why awareness is important for trace conditioning but not for delay conditioning.