Introduction to Adaptive Neurotechnologies

Introduction to Neurotechnologies

The human central nervous system (CNS) is the most convoluted known neural network. The inherent complexity of CNS poses serious challenges to studying its behavior as well as treating its anomalies. The longing for understanding the intricacies of the CNS, in tandem with the ever-increasing need for assisting patients who are suffering from debilitating neurological disorders, has been the principal driving factor for collaboration among engineers and scientists from different disciplines–this collective interdisciplinary endeavor gave rise to the field that is known as neurotechnology. Neurotechnology is an avant-garde, interdisciplinary field that employs state-of-the-art technologies to study and interact with the CNS. From different imaging, recording, and monitoring modalities to innovative neuromodulation techniques, neurotechnology embodies a broad range of methodologies.

Neuroimaging

Imaging is a crucial step in investigating both the physiological structure and the function of the nervous system.

Structural Imaging

Structural imaging techniques allow for studying anatomy, configuration, and structure of the nervous system on different scales. Here we introduce two common imaging techniques for studying the macroscopic structure of the brain and the spinal cord.

Computed Tomography (CT)

Computed tomography (CT) is a noninvasive imaging technique that can produce detailed images of internal organs, bones, soft tissue, and blood vessels (Toga). Although the term "Computed tomography" might refer to a group of imaging techniques such as Positron Emission Tomography or Single-Photon Emission Computed Tomography (in the most general sense) SPECT), here we only use it to refer to X-ray CT scan. A CT of the brain (and in general any other tissue) entails two steps: in the first step, the scanner uses a rotating X-ray beam to generate cross-sectional images—or "slices—of the brain. These 2D images are called tomographic images, and they are more informative than conventional X-rays. In the next step, a computer stacks successive slices and creates a 3D image of the brain. CT scan of the brain allows for easier identification and location of basic structures and possible tumors or abnormalities (Toga).

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is another noninvasive imaging technique that creates a high-definition 3D image of the brain or other internal organs (Toga). The underlying mechanism of MRI is based on the intrinsic magnetic properties of fundamental particles and, in particular, the hydrogen atoms in water molecules. In the presence of a uniform external magnetic field, a secondary nonuniform magnetic field with a certain gradient can be used to evoke electromagnetic radiation, which will reveal the configuration of these atoms (Bruggen). MRI can be used in two main modes: T1-weighted modes are used to detect the water content of tissues, and T2-weighted modes are used to study the fatty tissues. MIR has a much better resolution compared to CT. While brain CT scan is generally used to diagnose acute bleeding or skull fracture, MRI is the ideal method for visualization of more chronic pathological conditions (Hurley).

Functional Imaging

Functional imaging techniques allow for recording and studying the functionality of different parts of the nervous system. There are two general approaches to functional imaging direct and indirect. The former approach is based on capturing the electrophysiological signals which are a direct indication of neuronal activities, and the latter is based on measuring the hemodynamic signals which are the secondary indication of neuronal activities. Here we briefly introduce two common modalities.

Electroencephalography (EEG)

Electroencephalography (EEG) is a noninvasive recording technique that allows capturing large-scale brain signals from the surface of the scalp. EEG signals primarily reflect the synaptic potential of cortical neuronal populations that fire in a synchronous mode. Due to the excitable nature of neurons measuring their electrical activities is considered a direct approach to study their functioning. The intracranial EEG– also known as Electrocorticography (ECoG)–uses implanted electrodes to capture the electrical activities directly from the surface of the cortex.

functional Magnetic Resonance Imaging (fMRI)

functional Magnetic Resonance Imaging (fMRI) is the most common technique for recording the hemodynamic activity of the nervous system. fMRI measures the blood-oxygen-level-dependent (BOLD) signals which is an indirect approach to identifying which area of the brain has a relatively higher activity. The idea behind these groups of imaging techniques is that measuring the contrast in BOLD signals allows for identifying the more active regions in the network that are consuming higher levels of oxygen and thus receive more blood flow. While fMRI and other recording modalities based on BOLD signals enjoy a high spatial resolution, the indirect nature gives them a lower temporal resolution compared to direct functional imaging techniques such as EEG and ECoG.

Introduction to Adaptive Neurotechnologies

Adaptive neurotechnology (AN) is a well-established branch in the field that allows for developing neuro-assistive and neurorehabilitation systems. At the very core, the functionality of these systems relies on the direct, closed-loop interaction with the nervous system in real-time and requires three basic steps:

• Recording and processing the neuronal activities, e.g. electrophysiological or hemodynamic signals.
• Translating the biosignals into the desired output, e.g. command for robotic systems or prosthetics.
• Improving performance via neurofeedback and neuromodulation

Fulfillment of these basic steps is typically achieved by Brain-Computer Interfaces (BCI) which are the integral components in AN. Five principal application areas can be envisioned for BCI-based AN:

1. Replacing lost capabilities, such as spelling
2. Restoring lost functions, such as grasping
3. Improving functions, such as upper limb movement
4. Enhancing natural functions, such as error detection
5. Supplementing natural function, such as a future “third hand”

File:Wolpaw adaptive cycle.pdf