Formation Of Neural Assemblies Research Articles

Temporal patterns of synchrony in a pyramidal-interneuron gamma (PING) network.

Synchronization in neural systems plays an important role in many brain functions. Synchronization in the gamma frequency band (30-100 Hz) is involved in a variety of cognitive phenomena; abnormalities of the gamma synchronization are found in schizophrenia and autism spectrum disorder. Frequently, the strength of synchronization is not high, and synchronization is intermittent even on short time scales (few cycles of oscillations). That is, the network exhibits intervals of synchronization followed by intervals of desynchronization. Neural circuit dynamics may show different distributions of desynchronization durations even if the synchronization strength is fixed. We use a conductance-based neural network exhibiting pyramidal-interneuron gamma rhythm to study the temporal patterning of synchronized neural oscillations. We found that changes in the synaptic strength (as well as changes in the membrane kinetics) can alter the temporal patterning of synchrony. Moreover, we found that the changes in the temporal pattern of synchrony may be independent of the changes in the average synchrony strength. Even though the temporal patterning may vary, there is a tendency for dynamics with short (although potentially numerous) desynchronizations, similar to what was observed in experimental studies of neural synchronization in the brain. Recent studies suggested that the short desynchronizations dynamics may facilitate the formation and the breakup of transient neural assemblies. Thus, the results of this study suggest that changes of synaptic strength may alter the temporal patterning of the gamma synchronization as to make the neural networks more efficient in the formation of neural assemblies and the facilitation of cognitive phenomena.

Exploring a Quantum-Hebbian Approach Towards Learning and Cognition

Cognition, in all its diverse forms, can be attributed to the formation of specialized neural circuits in the brain. While in response to conscious experiences, arising due to sensory stimulation, neural assemblies are formed, conscious experience is itself an outcome of sustained synchronous firing of a neural assembly. This leads to a paradoxical situation or Neural Development Paradox: what comes first the conscious experience or the neural assembly? To have zero-lag synchronous activity amongst neurons of an assembly, which is needed for binding individual responses into a conscious percept, we need a very rapid source of communication between them. Axonal conduction delays amounting to several tens of milliseconds cannot account for the zero-lag synchrony across spatially separated brain an area that is required for STDP Hebbian learning to hardwire a neural assembly. Hence, an alternate means of instantaneous communication needs to be explored. According to the Penrose-Hameroff Quantum Approach towards consciousness, the microtubule cytoskeleton acts as a quantum computer whose collapsed states are conscious experiences manifesting in the form of an activated neural assembly. Neurons, whose microtubules are entangled, get connected by means of gap junctions, behaving like one giant neuron, firing in synchrony, seemingly breaking the Neural Development Paradox. By mental force of directed attention, Quantum Zeno effect can be instigated, as suggested by Von Neumann-Stapp, causing the activated state of the brain to stabilize till Hebbian learning strengthens the synaptic connections, giving way to a quantum explanation for the formation of neural assemblies, both intra-modality as well as inter-modality. In this paper we report our efforts towards building a simulation-mathematical model of Quantum-Hebbian Learning that attempts to interface classical Hebbian learning with quantum theoretic mechanisms of conscious experience to develop neural assemblies. Under the influence of a modulatory mental force of directed attention, the model is also able to address high level issues like mind wandering, zombie modes, volition etc. The model is an attempt to study the benefits of introducing the concept of duality in the formation of neural assemblies and understand how consciousness and attention influence the development of the brain. NeuroQuantology | September 2013 | Volume 11 | Issue 3 | Page 416-425