spectra    Publications

July 1st ~ Aug 30th

written by John Heo      Reviewed by Dr. Marianne Bezaire

ABSTRACT 

Glial cells, otherwise known as helper cells, are highly responsible for cleaning up axons and cell debris to maintain a healthy nervous system. They perform a crucial job, removing extracellular glutamate to regulate ion channels and neuron communication. Comprising up to 80% of malignant brain tumors, glial cell derived glioma cells release large amounts of glutamate, where excessive accumulation of glutamate in synaptic space triggers excitotoxicity, a detrimental process where ion channels are over-activated. This leads to an excessive influx of sodium and calcium ions and subsequent postsynaptic failures in communication, memory, and learning. Using computational modeling, we investigated the effect of elevated levels of extracellular glutamate in communication frequency and signaling strength of neurons. Prolonged activation of ion channels was represented by increasing the decay time constant (tau) of an excitatory synapse. Communication frequency was measured by...

May 4th ~ July 13th

written by Julius Kim      Reviewed by Dr. Tae-sik Yoon

ABSTRACT 

In this paper, I will discuss the feasibility of solid state devices such as RRAM and PCRAM acting as a synaptic device. I will explain the basic function of a synapse and then introduce the basic theories of the way that an RRAM and PCRAM device changes its resistance or conductance. RRAMs that use the filament conduction mechanism won’t be sufficient to make a synaptic device because of the intrinsic small resistance gap between the Set and Reset state, and the resistance instability during its write and read states. On the other hand, PCRAM could be a much better synaptic device due to its wide resistance gap and stable resistance during its write and read function, despite of the one-way gradual resistance change done by the Set operation, whereas the Reset operation needs an incremental pulse to make the gradual change.