Basic Questions (from Squire and Kandel)

• how does memory work
• are there different kinds of memory
• what is their logic
• where in the brain do we learn
• where do we store what is learned as memory
• can memory storage be resolved at the level of individual nerve cells

Prior to the 19 century the early philosophical approaches used methods of introspection, logic, and argument to

• define broad constraints on knowledge and what was knowable
• determine what was innate or acquired

The late 19^th century brought quantitative study of mental processes

• The 1885, Hermann Ebbinghaus monograph On Memory described systematic measurement of memory in terms of accuracy, retention, and capacity. This work also revealed some basic properties of memory such as differences in duration and the impact of repetition on retention.
• In 1887 , Sergei Korsakoff published his work on a syndrome that established the use of memory disorders as a means of studying mnemonic processes.
• In 1890, William James wrote Principles of Psychology that outlined sharp distinctions between short (primary) and long (secondary) term memory.
• 1898, Edward Thorndike working under James published his work using animal subjects to study memory.

The 20^th century brought the behaviorists demonstrating systematic ways of modifying behavior.

• Around 1904 Pavlov published his work on classical conditioning, or the conditioned reflex establishing the basis for systematic control of behavior through learning.
• In 1911, Thorndike demonstrated the principles of trial-and-error learning or instrumental/operant conditioning.
• The work of John Watson, B.F. Skinner, and Clark Hull in the 1930’s and 40’s introduced highly systematic singular black-box rules of learning for explaining complex behavior.

A more cognitive approach evolved from the limitations apparent in the behaviorists paradigm

• Tolman (1949) argued for a more cognitive mechanism of learning in which different types of learning used different rules. He studied more complex tasks that required behavioral selection related to problem solving.
• In the 1950’s Frederic Bartlett examined memory of naturalistic scenes and stories in an effort to examine the cognitive complexities of memory.

In addition to this work examining the principles of learning at the behavioral level there was an effort to identify the mechanisms responsible for learning and memory at the neural level.

• In the 1890’s following his pioneering work in brain anatomy Ramon Cajal suggested that structural changes in the brain might underlie learning and memory.
• In 1897 Charles Sherrington named the "synapse" and suggested that it was a likely candidate for a structure related to learning and memory.
• Beginning in the 1920’s Karl Lashley began studying the effect of removal of different amounts of cerebral cortex on maze learning. From this work the idea of "mass action" was formulated in which brain function was non-localized.
• In 1938, the neurosurgeon Wilder Penfield demonstrated that electrical stimulation of the brain, in particular the temporal lobe, could elicit reports of memories, perceptions, and hallucinations including voices, images, and music.
• In 1949, Donald Hebb published his work the Organization of Behavior in which he argued that memory was held in cell assemblies distributed throughout the brain which was in part, a response to the earlier work of Lashley.

• In 1957, Scoville and Milner published their work examining the patient H.M. in which removal of regions of the medial temporal cortex led to profound loss in memory capabilies without loss in intellectual or cognitive abilies demonstrating clear functional heterogeneity within the brain in contrast to the earlier notions of Lashley.
• Subsequent work in the 1960’s by Brenda Milner demonstrated that procedural memory in H.M. was unaffected further demonstrating that different types of memory could be maintained by different brain regions.
• In 1967, Seymour Benzer working in the fruit fly Drosophila using chemical mutagenesis to alter the function of individual genes implicated specific proteins in behavior and introduced the use of molecular genetic approaches in the study of memory.

What is Learning and what is Memory?

Definition

• Learning is an adaptive change in behavior resulting from experience

From this the early behaviorists black-box view can be seen as

Experience -----------------à behavior 1

|----------à behavior 2

|----------à behavior 3

INPUT BLACKBOX OUTPUT

in which selection is based on consequence (e.g. reinforcement, Skinner).

• In non-associative learning, the adaptive advantage is already established.
• In more associative learning the extent of adaptive advantage must be evaluated.

Further refinement of this model in a reductionist direction can be described as

Experience ----à neural activity ----------à neural output pattern 1 ----à behavior 1

|----------à neural output pattern 2 ----à behavior 2

|----------à neural output pattern 3 ----à behavior 3

INPUT BLACKBOX OUTPUT

In which selection of neural patterns is based on consequence (e.g. reinforcement, Hebb)

This can be further reduced to the synaptic/molecular level in which the black box falls at the synaptic interface between cells.

In addition to the reductionist refinement of the process of learning at more cellular levels, there has been an elaboration of learning along the dimension of regional or functional heterogeneity.

/----à neural activity -------à neural output pattern 1’ ----à behavior 1’

/

/

/

Experience ----à neural activity ----------à neural output pattern 1 ----à behavior 1

|----------à neural output pattern 2 ----à behavior 2

|----------à neural output pattern 3 ----à behavior 3

Let us examine a simple definition of memory

Definition

• Memory is the retention of learning

A function of memory is to allow production of learned/adaptive behavior at a later time.

But the adaptive response may not be the same as the original learned behavior

Note that our simple description of the learning process involved the selection of behavior based on the evaluation of consequence.

Memory also involves a process by which past experience can be used to guide future adaptive behavior.