In addition to biocompatibility, once the implant is in place, the body may have an adverse reaction to it over an extended period of time, rendering the implant useless. Implanting a microelectrode array can cause damage to the surrounding tissue. Development of scar tissue around the electrodes can prevent some signals from reaching the neurons the implant is meant to. Most microelectrode arrays require neuronal cell bodies to be within 50 μm of the electrodes to provide the best function, and studies have shown that chronically implanted animals have significantly reduced cell density within this range. Implants have been shown to cause neurodegeneration at the site of implantation as well. Neural coding represents a difficulty faced by cortical implants, and in particular, implants dealing with cognition. Researchers have found difficulty in determining how the brain codes distinct memories. For example, the way the brain codes the memory of a chair is vastly different from the way it codes for a lamp. With a full understanding of the neural code, more progress can be made in developing a hippocampal prosthetic that can more effectively enhance memory. Due to the uniqueness of every patient's cortex, it is difficult to standardize procedures involving direct implantation. There are many common physical features between brains, but an individual gyrus or sulcus (neuroanatomy) can be different when compared. This leads to difficulties because it causes each procedure to be unique, thus taking longer to perform. In addition, the nature of a microelectrode array intended effect is limited due to the stated variance's presented in association with individual cortex uniqueness i.e. differences. Present day microelectrode arrays are also constrained due their physical size, and achievable data processing/capability rates; which continue to be governed in relation to the characteristics dictated in accordance with Moore's Law. As more research is performed on, further developments will be made that will increase the viability and usability of cortical implants. Decreasing the size of the implants would help with keeping procedures less complicated and reducing the bulk. The longevity of these devices is also being considered as developments are made. The goal with the development of new implants is "to avoid the hydrolytic, oxidative and enzymatic degradation due to the harsh environment of the human body or at least to slow it down to a minimum which enables the interface to work over a long time period, before it finally has to be exchanged." With extended operational lifetimes, fewer operations would need to be performed for maintenance, allowing for The amount of polymers that are now able to be used for neural implants has increased, allowing for a greater diversity of devices.