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Neuroscience is the scientific study of the neurons, the functional neuron circuits in the brain, and the nervous system. Nanotechnology, on the other hand, is a science that utilizes nano-sized materials with unique physiological properties such as chemical reactivity, durability, conductivity, and strength.
Such nanomaterials are already being used in the fields of electronics, cosmetics, and medicines, but when used in neuroscience, they form the so-called field of Nanoneuroscience. Due to the microscopic size of the neurons within the human body, the use of nanotechnology for controlling neurons, and thus neural circuits, has been a topic of interest to many neuroscientists.
The idea of using various modes of technology for controlling the human brain and behavior is not new. In fact, scientists have long been trying to find ways of amending and improving the function of the neural system. With the existence of innumerable neurological conditions, diseases, and injuries such as neurodegenerative, neurodevelopmental conditions, brain injuries and cancer, the quest for finding a cure or a solution is becoming more and more urgent.
The use of traditional technologies such as transcranial Direct Current Stimulation (tDCS) and Transcranial Magnetic Stimulation (TMS) for increasing or decreasing the firing activity of neurons is not novel and has been broadly used in research. Even though studies show that these can be effective in modulating and controlling neuronal activity, it is worth highlighting the practical discomforts associated with the use of these methods.
To begin with, in order for the neurons in the brain to be influenced, and their activity – changed, a prolonged neural stimulation is required. tDCS relies on electrodes and wires in order to perform, while TMS requires a big and heavy magnetic coil, plugged into a battery in order to apply a magnetic field. Furthermore, due to their rather big size, TMS and tDCS can occasionally, unintentionally, stimulate neighboring neurons to the one or the group initially targeted, and therefore, the precision of such types of indirect neural stimulation is not ideal.
A solution to all of the problems mentioned above comes from the use of nanotechnology for neuron stimulation.
Since the size of nanomaterials is nanoscopic enough, 1-100 nm, these can be directly applied to site-specific neurons, eliminating the problem associated with the potential stimulation of untargeted neurons and neuronal groups. The client comfort is not compromised as this type of nanotechnology does not require wires and batteries to be attached or linked to the invention of interest.
Prolonged stimulation is therefore not a challenge as there are no batteries or wires that can malfunction or deplete themselves. One example of such nanoneuroscience technology is Optogenetics.
Optogenetics has seen great development and better understanding in recent years. At the heart of the concept of applying Optogenetics for neuroscience purposes, is the idea that we can selectively target and activate or inhibit specific neurons or groups of neurons within an in vivo environment through the use of light, in a way that allows leaving neighboring neurons intact. In a simpler language, neurons and their activity can be turned on and off using molecular neuronal activity “switches”.
This complex, in its essential function, is performed by microbial, light-sensitive ion conductance regulating proteins. These proteins are introduced individually into specific groups of neurons in the brain and become part of the cell system. Once in the brain, the ion flux regulating the activity of the proteins can be controlled externally, using light pulses targeted at single or multiple neurons, without interfering with the activity of the surrounding untargeted neurons. Different ion channels have different light thresholds of activation and therefore have different activation requirements.
Ion proteins are typically activated through the delivery of visible light (~400-600 nm) to the neurons. For example, channelrhodopsin-2 (ChR2) is a cation channel with an activation threshold of 470 nm of blue light. Once activated, the channel allows sodium ions to pass the membrane and enter the neuron. This process then increases the excitability of the neuron and therefore makes it fire at a higher rate, causing increased action potentials. Another example is halorhodopsin (NpHR). NpHR is a chloride pump that is activated by ~580 nm yellow light. Contrary to ChR2, NpHR pumps chloride anions into the neuron, thus inhibiting the neuron and decreasing its firing and action potentials.
Despite the findings above, the delivery of visible light to deeper neurons has proved to be a challenge, as visible light is highly scattered in tissue and therefore does not always reach the deeper layers of the brain. Upconverting nanoparticles (UCNPs) seem to be the solution to this problem. UCNPs absorb near-infrared light at a higher wavelength than the one required for the activation of the ion proteins of deeper neurons. This near-infrared light then undergoes certain absorption and transformation in the brain tissue, and by the time it reaches the targeted deeper tissue neurons, it emits the blue light required for the neuron activation.
As promising as the use of Optogenetics might seem in correcting for malfunctioning neurons, it is obvious that there is a long way for research to go before scientists can use this method in developing treatments for neurological conditions and injuries in humans. Yet, Optogenetics is a topic worth keeping an eye for in future biochemistry and medical research.