Cognitive enhancement is the use of any instrument, device, or technique to improve cognitive functions such as attention, memory, or reasoning. It can be used for therapeutic purposes in the treatment of a number of conditions including attention-deficit hyperactivity disorder (ADHD), Alzheimer’s disease, and schizophrenia.
Cognitive rehabilitation is a process that helps people with cognitive impairments to recover lost skills and abilities. The goal is to improve the person's quality of life and their ability to function in society.
Virtual reality (VR) provides a real-time, immersive experience to users in a computer-generated world. In consumer-level VR, gaming is the most common application. However, VR has many applications in different industries. Thanks to those applications, multi-sensor applications are growing, and they are aiming to provide end-user highly interactive and emotional experiences.
We can categorize the multi-sensor applications in four categories :
1. VR Treadmills: Allowing end-user walking in the computer-generated World without any accident. Mostly commercial products and highly expensive for consumer market. Two of the important examples are Kat-VR  (company has both consumer and enterprise products) and Infinadeck  omnidirectional treadmill (product is only available for enterprise market).
2. Haptic Gloves: Aiming to simulate feeling (e.g., feeling wet during your arms in a water) of objects via sensors. Those applications are exceeding motion controllers about feel and motion detection accuracy via external skeleton. Haptx  is a great example for haptic gloves. Like treadmills, haptic gloves are commercial products too.
3. Haptic Vests: Like gloves, haptic vests are aiming to simulate feelings on human body in a virtual environment. There are numerous consumer products in this category. Tesla Suit  is great example for both commercial and consumer usage of haptic vests.
4. Full Body Tracking: Aiming to detect and monitor all movements in human body. There are couple of ways to achieve that target. Pucks and camera systems are common examples. NHL is a great example for commercial use. NHL is planning to track body movements of players via puck trackers.  One of the main developments in this area is Neuralink which is created by Elon Musk. Company is aiming to create brain-computer interaction via surgically installed implement.
Multi-sensor applications are commonly use in enterprise market for training purposes. Projects like Neuralink is creating new possibilities in VR. Neuralink is aiming create science-fiction like capabilities, fixing neurological disorders and enhanced the brain. On trials on pigs, Neuralink detects the body movements of pig with a great accuracy. Company is targeting to reach read-write operations on human brain to fix neurological problems. 
II. Cognitive Enhancement and Biomedical Applications
Neurotechnology is the next big thing in the world of medicine. The use of virtual reality and augmented reality are becoming more common in diagnosing and treating patients.
The use of VR headsets, for example, can help with cognitive rehabilitation. It can be used to train patients to relearn how to do certain tasks that they may have lost because of an injury or illness.
The use of virtual reality (VR) has been found to be effective in treating mental health disorders such as post-traumatic stress disorder (PTSD), anxiety, phobias and depression. VR also has applications in diagnosis and cognitive rehabilitation which are still being explored by researchers.
Biomedical applications in virtual reality are emerging and revolutionary in many fields in medicine. Theoretically, if you have a brain problem in real life, this could be simulated in virtual reality. This would allow you to "practice" your brain before actually having the surgery or going through trauma. This is beneficial for patients because they will know what to expect and not be scared, which would help their recovery process.
Neuralink can be our future but today virtual reality is wide usage in patient training, tracking, diagnostic and cognitive rehabilitation purposes. Germany based company VReha can be a great introductory example of usage of VR in biomedical applications. With the development of neurological diseases such as dementia and Alzheimer, we are losing our cognitive capabilities especially in older ages.
Basically, VReha is a VR application for diagnostic of diseases and rehabilitation of patients in virtual environment. Normally, traditional tests are paper pen based, highly abstract and costly for patients. Application is allowing patients to deal with everyday tasks and monitor body movements for diagnostic and rehabilitation purposes. 
When we talk about immersive environment (VE), we refer to those in which the sensory information is compelling enough to create perceptions of being physically present within the virtual environment. It can be mix of any form of modality, not just a visual. For example, musical recordings can be though as an aurally rendered VE or smell-touch of something can be seen as augmented VE. 
Like in the VReha example, usage of VEs with great tracking and monitoring features, allowing us to diagnose and treat neurological diseases. I tried to collect some of the usage areas in neurology in Table 1 below.
Exposure therapies are common in phobia and anxiety treatment.
Another important development in the field is, researchers found that areas of the brain responsible for identifying and signaling pain have a decrease in activity while the patient is in a immersive VE. Cedars-Sinai Hospital in California, USA is providing virtual therapy for pain management.
III. Final Thoughts
Virtual reality therapies in various topics and cognitive enhancement applications are proven methods and promising for the future. In the first two sections, we saw that main application areas in medicine are diagnostic, therapy and rehabilitation. VR is a relatively new field in medicine. There is no long history to draw from. However, today we can see VR as an accelerator for any neurological treatment. With projects like Neuralink, we can use VR to deep dive into brain-computer interaction and actually cure diseases like Alzheimer. Like vaccination in COVID-19 pandemics, we should spread the use of VR in medicine and monitor the results to create better and more personalized treatment plans.
Further Readings & References
 Future Tech of Virtual Reality, Youtube, Virtual Insider, April 2020  KAT-VR, Company Website, March 2021  Infinadeck, Company Website, March 2021  Haptx, Company Website, March 2021  Tesla Suit, Company Website, March 2021  NHL Plans to Deploy Puck and Player Tracking Technology Next Season, News, NHL Website, January 2019  Neuralink — Catalyst For Full Dive VR?, Youtube, Pezle, March 2021  VReha: Virtual Realities For Digital Diagnostics and Cognitive Rehabilitation, Youtube, MPI für Kognitions- und Neurowissenschaften, May 2020  Virtual Reality for Psychological and Neurocognitive Interventions, Rizzo A., Bouchard S., Book, p[17–31] ,2019  Virtual Reality As A Tool For Fighting Addiction, Youtube, TedX Talks, March 2017  Can Virtual Reality Help Fight The Oploid Crisis?, Youtube, Freethink, February 2019