## 1 Introduction  
The most complex organ in humans is the central nervous system (CNS). It controls most of the human functions. Its function controls all aspects of our behavior such as breathing, feelings, etc. [1]. Brain diseases can occur as a result of the interactions of the brain with several complex environmental factors [2]. Neurodegenerative disorders are becoming more widespread in society especially the elderly age group. Neurodegenerative disorders result in disability and death worldwide [3]. These diseases presently affect more than 1 billion people worldwide [4]. Currently, these diseases represent a major medical challenge and there is a need for therapeutics which are effective and can overcome the global burden of neurodegenerative disorders [5]. Some of the challenges associated with therapeutics used to treat neurodegenerative disorders are severe effects such as diabetes, dizziness, seizures, Stevens-Johnson syndrome, and toxicity, etc. [6]. Development of drug delivery systems is one approach which has the potential to overcome the pharmacological limitations associated with therapeutics used to treat neurodegenerative disorders [7]. Some delivery systems used for the delivery of drugs to the brain are liposomes, in situ gel, nanogels, nanoparticles, micelles, emulsions, dendrimers, etc. [8]. Most of the aforementioned systems have been effective in transporting bioactive agents across different models of blood-brain barrier (BBB) by known mechanisms in vitro and in vivo. Some of the aforementioned drug delivery systems have also been reported to display good preclinical outcomes which indicate their potential application for the management of conditions such as stroke,HIV (Human Immunodeficiency Virus), Alzheimer's disease, brain tumors, etc. [9]. However, in the design of these drug delivery systems for brain targeting, factors to be considered are the particle size, their stability in physiological circulation, surface affinity, etc. [10]. In the application of nanoparticles for brain targeting, their drug release profiles have been reported to be sustained, slow, and controlled, thereby overcoming toxicity. Nanoparticles also target specific brain sites which indicate their capability to cross the blood-brain barrier which is attributed to their nano size [11]. Nanosized polymer-based carriers are potential systems for targeted delivery of potent drugs to the brain due to some of their properties such as the protection of the drugs from biological processes which can decrease the drug bioavailability, and their capability to cross the BBB [12]. Several targeted drug delivery systems and imaging devices developed for the treatment and diagnosis of brain diseases have been studied [13]. According to the World Health Organization (WHO), over 50 million people suffer from epilepsy globally. Globally, an estimation of approximately 2.4 million people are diagnosed with epilepsy each year [14]. [PERSON]'s disease (PD) is reported to be common among the elderly [15]. Due to the high rate of people living with brain diseases, there is a need for the development of effective therapeutics that can penetrate the BBB. The development of drug delivery systems that can deliver drugs across the blood-brain barrier is a potential approach for the treatment of neurodegenerative disorders. This review article reports the efficacy of chitosan in the development of drug delivery systems for brain targeting.