With the rapid criminalization of our civilization, people are getting more and more involved in un-lawful (criminal) activities and law enforcement agencies are facing a great difficulty in bringing the culprits/convicts to the final judgment of court. Days are gone when simple methods of coercing, eye to eye contact effect and fear of supernatural/religious powers were effective on such people (criminals/convicts) for extraction of truth. The search for effective aids of interrogation is probably as old as man’s need to obtain information from an uncooperative source and as persistent as his impatience to shortcut any tortuous path. 

Following the scientific approach to catch the signals from the criminals to proceed further, development of new tools of investigation has led to the emergence of scientific tools of interrogation like the psychological tests, narco test and polygraphic tests and many more. These methods of interrogation are very much in use these days but their reliability in courts is still an issue. Such tests generally don’t have legal validity in court and these tests can only assist police investigations. Law is a living process, which changes according to the changes in society, science, ethics and so on. The legal system should imbibe developments and advances that take place in science as long as they do not violate fundamental legal principles and are for the good of the society. Such advances in science and technology are always countered by the mastermind criminals and hence these lie detection tests are also proving to be a useless exercise particularly in cases of master-mind criminals. Various new scientific technologies are catching up which may shortly become alternatives to the traditional lie detection methods. Here some prevailing and some coming up methods of lie detection are discussed.

Psychological test:

Psychological tests are usually administered and interpreted by a psychologist. Psychologicaltests assess and evaluate information that is given by the criminal to the examiner and aren’t magic. The information is taken either in the form of answers to interview questions or as answers on paper—or on a computer—to specific questions. Ultimately, a physiological test’s accuracy depends on how carefully and seriously the answers are given. Hence, no psychological test is ever completely valid or reliable because the human psyche is just too complicated to know anything about it with full confidence. That’s why there can be such uncertainty about a case even after extensive testing.

Narco test:

The term Narco-Analysis is derived from the Greek word “nark” (meaning "anesthesia" or "torpor") and is used to describe a diagnostic and psychotherapeutic technique that uses psychotropic drugs, particularly barbiturates, to induce a stupor in which mental elements with strong associated affects come to the surface, where they can be exploited by the therapist. The narco analysis test is conducted in order to lower a subject's inhibitions by interfering with his nervous system at the molecular level, in the hope that the subject will more freely share information and feelings. In this state, it becomes difficult though not impossible for him to lie. The subject is not in a position to speak up on his own but can answer specific but simple questions. The answers are believed to be spontaneous as a semi-conscious person is unable to manipulate the answers. However, crime branch officials have found that key suspects took anaesthetic drugs (like Catamine, Propofol, Pentothal and Fortwin) to cheat narco tests, in case they were arrested. Regular use of the drugs made them immune to narco tests. This effectively puts a question mark on all 'revelations' made during narco tests so far.

Polygraph Test:

Polygraph machines are essentially biofeedback devices. It is an examination, which is based on an assumption that there is an interaction between the mind and body and is conducted by various components or the sensors of a polygraph machine, which are attached to the body of the person who is interrogated by the expert. The machine records the blood pressure, pulse rate, respiration, muscle movements and electrical resistance of the skin. Polygraph test is conducted in three phases- a pretest interview, chart recording and diagnosis. Even with a trained and skillful administrator, polygraph technology is not altogether perfect at detecting lies. There is a lot of variability in how different people react when lying first of all. The act of being measured tends to produce anxiety which creates the potential for false positives. The worst part is that there are people out there who are so good at lying that they believe their own lies (or at least are in large part nonreactive) and thus don't perturb the polygraph.

The Brain Mapping Test (P300):

In this method, called the “brain-wave finger printing”; the accused is first interviewed and interrogated to find out whether he is concealing any information. Then sensors are attached to the subject’s head and the person is seated before a computer monitor. He is then shown certain images or made to hear certain sounds. The sensors monitor electrical activity in the brain and register P300 waves, which are generated only if the subject has connection with the stimulus i.e. picture or sound. The subject is not asked any questions here.

Functional magnetic resonance imaging (fMRI):

In functional Magnetic Resonance Imaging experiments, the subject usually alternates between performing a mental task and resting (or undertaking an alternative task) while repeated images of the brain are rapidly acquired. Areas of the brain in which there are strong correlations between the performance of the task and the MRI signal time course are then identified as having been involved in that task. When the subject starts to perform the task, neuronal activity increases in those parts of the brain required. These areas require additional energy, which is provided by an increase in the regional blood supply. This increase in blood flow leads to an increase in the blood oxygenation level, which in turn changes the magnetic properties of the blood and hence the MRI signal. Unfortunately, fMRI, as it is used today, has a major drawback: it measures blood flow, or hemodynamics, which is an indirect measure of neural cell activity. It turns out hemodynamics basically introduces a delay of five seconds. It keeps away from being able to detect fast variation.  Since neurons typically fire on the order of milliseconds, current fMRI techniques provide only a rough estimate of what the brain is doing at any given moment. FMRI scans also have a relatively low spatial resolution, measuring activity in areas of 100 microns, a volume that typically contains 10,000 neurons, each with varying activation patterns. Efforts to fine-tune fMRI have focused on developing stronger magnets

Calcium Tracking:

Research have found that tracking calcium, a key messenger in the brain, may be a more precise way of measuring neural activity, compared with current imaging techniques (viz. fMRI). When a neuron sends an electrical impulse to another neuron, calcium-specific channels in the neuron's membrane instantaneously open up, letting calcium flow into the cell. It's a very dramatic signal change. Fluorescent calcium sensors are already used in superficial optical imaging, but haven't yet been applied to the deeper brain tissues that are accessible via the powerful magnets of fMRI machines.

Electro EncephaloGram(EEG):

Brain emits electrical signals called event-related potentials (ERPs) that can be tracked with a high-density electroencephalogram (EEG) machine and sensors attached to the face and scalp. Telling the truth and then a lie can take from 40 to 60 milliseconds longer than telling two truths in a row, because the brain must shift its data-assembly strategies. Psychologists working on the technology believe it is 86% accurate.

Eye Scans:

The stress that creates the clues picked up by polygraphs also boosts blood flow in capillaries around the eye. A new application of thermal-imaging technology, called periorbital thermography, uses a high-resolution camera to detect temperature changes as small as .045°F (.025°C). Scientists are also developing technology to track and interpret the motion of the eyes. When the eye takes in a series of images of faces, objects or scenes, it spends less time on familiar elements because the brain needs less processing to interpret them.

Micro expressions:

Scientists agree that the face tells tales about the person. Psychologist are busy in codifying facial movements into microexpressions called the Facial Action Coding System (FACS). FACS is the most promising lie detection technology which is the least technologically dependent. It costs much less than other "device-oriented" techniques, and is much easier to train people to use it. It is also the only technique that can be easily used in a natural setting.

Scanning Brain with Light:

A new noninvasive diagnostic technology could give the single most important sign of brain health: oxygen saturation. A standard pulse oximeter is clipped onto a finger or an earlobe to measure oxygen levels under the skin. It works by transmitting a beam of light through blood vessels in order to measure the absorption of light by oxygenated and deoxygenated hemoglobin. The information allows physicians to know immediately if oxygen levels in the patient's blood are rising or falling. New device uses a technique called ultrasonic light tagging to isolate and monitor an area of tissue the size of a sugar cube located between 1 and 2.5 centimeters under the skin. The probe, which rests on the scalp, contains three laser light sources of different wavelengths, a light detector, and an ultrasonic emitter. The laser light diffuses through the skull and illuminates the tissue underneath it. The ultrasonic emitter sends highly directional pulses into the tissue. The pulses change the optical properties of the tissue in such a way that they modulate the laser light traveling through the tissue. In effect, the ultrasonic pulses "tag" a specific portion of tissue to be observed by the detector. Since the speed of the ultrasonic pulses is known, a specific depth can be selected for monitoring. The modulated laser light is picked up by the detector and used to calculate the tissue's color. Since color is directly related to blood oxygen saturation, it can be used to deduce the tissue's oxygen saturation.

The measurement is absolute rather than relative, because color is an indicator of the spectral absorption of hemoglobin and is unaffected by the scalp. Deeper areas could be illuminated with stronger laser beams, but light intensity has to be kept at levels that will not injure the skin. Given the technology's current practical depth of 2.5 centimeters, it is best suited for monitoring the upper layers of the brain. While the technology is designed to monitor a specific area, it could also be used to monitor an entire hemisphere of the brain. Measuring any area within the brain could yield better information about whole-brain oxygen saturation than a pulse oximeter elsewhere on the body would.