| dc.description.abstracteng | Memory serves to process and store information about experiences such that this information can be
used in future situations. The transfer from transient storage into long-term memory, which retains
information for hours, days, and even years, is called consolidation. In brains, information is primarily
stored via alteration of synapses, so-called synaptic plasticity. While these changes are at first in a
transient early phase, they can be transferred to a late phase, meaning that they become stabilized
over the course of several hours. This stabilization has been explained by so-called synaptic tagging
and capture (STC) mechanisms. To store and recall memory representations, emergent dynamics arise
from the synaptic structure of recurrent networks of neurons. This happens through so-called cell
assemblies, which feature particularly strong synapses. It has been proposed that the stabilization
of such cell assemblies by STC corresponds to so-called synaptic consolidation, which is observed in
humans and other animals in the first hours after acquiring a new memory. The exact connection
between the physiological mechanisms of STC and memory consolidation remains, however, unclear.
It is equally unknown which influence STC mechanisms exert on further cognitive functions that guide
behavior. On timescales of minutes to hours (that means, the timescales of STC) such functions include
memory improvement, modification of memories, interference and enhancement of similar memories,
and transient priming of certain memories. Thus, diverse memory dynamics may be linked to STC,
which can be investigated by employing theoretical methods based on experimental data from the
neuronal and the behavioral level.
In this thesis, we present a theoretical model of STC-based memory consolidation in recurrent networks of spiking neurons, which are particularly suited to reproduce biologically realistic dynamics.
Furthermore, we combine the STC mechanisms with calcium dynamics, which have been found to
guide the major processes of early-phase synaptic plasticity in vivo. In three included research articles as well as additional sections, we develop this model and investigate how it can account for a
variety of behavioral effects. We find that the model enables the robust implementation of the cognitive memory functions mentioned above. The main steps to this are: 1. demonstrating the formation, consolidation, and improvement of memories represented by cell assemblies, 2. showing that
neuromodulator-dependent STC can retroactively control whether information is stored in a temporal
or rate-based neural code, and 3. examining interaction of multiple cell assemblies with transient and
attractor dynamics in different organizational paradigms.
In summary, we demonstrate several ways by which STC controls the late-phase synaptic structure
of cell assemblies. Linking these structures to functional dynamics, we show that our STC-based model
implements functionality that can be related to long-term memory. Thereby, we provide a basis for the
mechanistic explanation of various neuropsychological effects. | de |