The paper's first section reviews the theories of how the polygraph detects deception that emerged in the early 1990s. These include the measurement of physical reactions related to the fear of punishment (threat-of-punishment theory); physical reactions related to conflicting emotions (conflict theory); conditioned physical responses related to telling a lie in response to a direct question (conditioned response theory; and different physical responses when a person tells the truth and lies (arousal theory). The paper's second section reviews theories of the polygraph that were developed in the early 21st century. These include an attempt to integrate theories developed in the 1990s (mental attitude theories); varying physical reactions to the stimuli of control and test questions (orienting theory); and physical reactions to various types of memories (memory traces identification). The last two sections of the paper focus on work done by Russian scientists in relation to the physical phenomena associated with deception. The work of these scientists focused on memory as having a fundamental role in the mechanisms of lie detection. The author supports the task-oriented memory test theory as the best fit for explaining the scientific data on physical reactions to deception. Under this theory, the test and control questions of the polygraph examination are stimuli that trigger memories of particular events. Stimuli that trigger memories the subject wants to hide evoke distinctive physiological reactions that can be measured by the polygraph. 62 references