Sealdah court on Thursday reportedly gave permission to the Central Bureau of Investigation (CBI) to conduct a polygraph test on former principal of RG Kar Medical College and Hospital, Sandip Ghosh and four other interns of the college in connection with the rape and murder of the 31-year old trainee doctor.

The development came after Supreme Court Justice J.B. Pardiwala on Thursday told the CBI counsel that the agency "must pursue" the polygraph test permission from the Calcutta court.

The CBI has been interrogating Ghosh for six days. The Calcutta high court ordered a CBI inquiry into the rape and murder incident at RG Kar.

A polygraph test is a lie detector test. A psycho- biological examination using computerised technology that checks the veracity of statements of person questions.

As per reports, John Augustus Larson, a medical student and officer at the Berkeley Police Department in California, invented the cardio-pneumo psychogram in 1921, a device that monitored systolic blood pressure and breathing depth, and recorded it on smoke-blackened paper.

The basis of the polygraph test is that when a person lies the body will observe changes. The changes in the nervous system are recorded by the investigative authorities.

The investigating officer and the specialist create questionnaires for the suspect.

Bodily changes, like respiration, skin resistance, blood pressure and pulse rate and temperature are noted down.

The polygraph test is effective for non-habitual criminals, as per a forensic expert’s website.

It is not known if the four interns are the same names (among the many others) who had been questioned earlier by the Kolkata Police in connection with the case.