Long-Term Memory, Simulated Qubits, Physical Qubits - Brain Theory from a Circuits and Systems Perspective - page 58

with a specified probability, as explained below. This is useful when probabilistic
processing is needed, as for certain types of memory search.
An important configuration of a recursive neuron is the controlled toggle,
examples of which are delineated below. A controlled toggle is also a basic memory
element, but must be toggled from its current value to its new logic value, and
cannot simply be set, or over written as though it were a random access memory
device.
This chapter begins with a discussion of basic memory elements, including long-
term potentiation (LTP) as the basis for an element of memory that holds a logic
value for an attribute with 100 % fidelity. A recursive neuron may also serve as a
basic memory element to hold a logic value for an attribute with 100 % fidelity. So
two possible styles of long-term attribute memory are presented below. Also
discussed below is the real possibility of a combination of these two types of
elements.
Neurons Configured into Elements of Memory
Associative search through the words of long-term memory and related subliminal
processing all depend on the availability of practical memory elements. In practice
these must store a logic value (a true) for attributes that are needed, and they must
have ability to return their information (to be read) by the system in a convenient
way. Pursuing these ground rules, this chapter introduces basic memory elements.
Two basic mechanisms for long-term memory are proposed: LTP and Recursive
Memory.
Memory Based on Long-Term Potentiation
This phenomenon is thought to be related to learning as well as to long-term
memory [ 2 ]. One may envision a memory subcircuit model as in Fig. 4.1 .
In this model a regular synapse S2 associated with (memory) neuron U2 is
pulsed (possibly in a certain way) many times via OR neuron U1. This makes U2
more receptive to being triggered. It is implied that the receptor in question is
susceptible to LTP. Subsequently a read signal (R) from a weak synapse results in a
weak query consisting of ideally, only one pulse, designated by Query(1), that,
although weak, will still produce a dendritic pulse burst. Without LTP there would
be no trigger, since ordinarily the capacitance of the receptor on U2 is such that it
needs to be charged by more than one pulse to result in triggering.
Note that this process is modeled with charge from pulses that accumulate in
membrane capacitance, as explained in a previous chapter. The geometry and the
membrane parameters of the receptor on its spine are such as to result in a slightly
higher capacitance that cannot be triggered by a single pulse. To ensure that the LTP