By Vibha Rana

The intersection of mental health and criminal responsibility has long been a contested domain in criminal law. The classical maxim actus non facit reum nisi mens sit rea which conveys that a mere act does not constitute guilt unless accompanied by a culpable state of mind serves as the foundation of criminal responsibility. However, when an accused suffers from mental illness or cognitive impairments, this presumption of a guilty mind becomes complicated. Indian criminal law has historically relied on the McNaughten rules of insanity to determine whether an individual can be held criminally responsible. With the advent of the Bharatiya Nyaya Sanhita, 2023 (BNS), Bharatiya Nagarik Suraksha Sanhita, 2023 (BNSS), and Bharatiya Sakshya Adhiniyam, 2023 (BSA), a new legal architecture is in place to address such questions. Yet, the challenge lies in reconciling these statutory frameworks with emerging neuro-legal evidence, which provides scientific insights into brain functioning and mental disorders.

THE INSANITY DEFENCE UNDER INDIAN CRIMINAL LAW

Courts in India have traditionally interpreted this provision strictly. In Dahyabhai Chhaganbhai Thakkar v. State of Gujarat (AIR 1964 SC 1563), the Supreme Court held that the burden of establishing legal insanity rests upon the accused; however, the degree of proof required is not as stringent as that in ordinary criminal cases. More recently, cases such as Surendra Mishra v. State of Jharkhand (2011) reiterated that medical insanity is distinct from legal insanity, the latter requiring proof that the accused was incapable of understanding the nature of the act at the material time.

PROCEDURAL SAFEGUARDS FOR MENTALLY ILL ACCUSED

The Bharatiya Nagarik Suraksha Sanhita (BNSS), 2023 now lays down procedures concerning accused persons with mental illness, largely corresponding to Sections 328–339 of the CrPC, 1973. Under Sections 367 to 378 of the BNSS, if an accused person is found to be of unsound mind, the magistrate is required to conduct an inquiry into their mental condition and, where necessary, refer them to an appropriate psychiatric facility for evaluation and treatment. These provisions aim to balance due process with the rights of mentally ill offenders, ensuring they are not subjected to unfair trials.

Importantly, the BNSS introduces a more structured approach to mental health assessments, emphasising medical board reports and psychiatric evaluations. However, in practice, implementation continues to be plagued by infrastructural deficits, lack of trained forensic psychiatrists, and delays in examination.

EVIDENTIARY DIMENSIONS OF MENTAL HEALTH DEFENCES

The evidentiary burden in cases of mental illness defence is regulated by Section 113 of the Bharatiya Sakshya Adhiniyam, 2023 (BSA) (previously Section 105 of the Indian Evidence Act, 1872). This section requires that the burden of proving the existence of circumstances bringing the case within the general exceptions, such as insanity, lies upon the accused. At the same time, if reasonable doubt arises regarding the accused’s mental state, the benefit must go to the accused, consistent with the presumption of innocence under Article 21 of the Constitution.

Neuro-legal evidence such as brain imaging, neuropsychological tests, and genetic markers is increasingly being invoked in courts worldwide to demonstrate diminished capacity, impulse control disorders, or psychiatric illnesses. While Indian courts have been cautious in admitting such evidence, the BSA provides a framework for the admissibility of scientific and expert evidence, which could pave the way for greater reliance on neuroscientific tools in future cases.

THE CONSTITUTIONAL BACKDROP: RIGHT TO FAIR TRIAL AND MENTAL HEALTH

The rights of mentally ill accused are rooted in constitutional guarantees under Articles 14, 19, and 21. The Supreme Court in Accused ‘X’ v. State of Maharashtra (2019) underscored the need to consider mental health as a mitigating factor in capital sentencing. The Court also linked access to mental healthcare with the right to life and dignity under Article 21. Additionally, the Mental Healthcare Act, 2017 reinforces the state’s obligation to ensure that persons with mental illness have a right to fair treatment, including within the criminal justice process.

NEURO-LEGAL EVIDENCE: A CHALLENGE TO TRADITIONAL DOCTRINES

Neuro-legal evidence challenges the binary nature of legal insanity. Whereas the McNaughten rule looks at whether the accused knew the nature of the act, neuroscience can reveal degrees of impairment, such as diminished responsibility or impaired impulse control, which may not fit neatly within Section 22 of BNS. For example, brain scans showing abnormalities in the prefrontal cortex can indicate impaired decision-making capacity, yet courts must grapple with whether such impairments absolve responsibility entirely or merely mitigate culpability.

This raises pressing questions: Should India move beyond the rigid McNaughten framework to recognise gradations of culpability based on neuroscientific insights? Should sentencing take into account neurobiological predispositions to certain behaviours?

JUDICIAL APPROACH IN INDIA AND ABROAD

While Indian courts have so far adhered to the classical test, international trends indicate a gradual shift. In the United States, for instance, neuroimaging evidence has been considered in capital sentencing to argue for mitigating factors. In the UK, diminished responsibility as a partial defence acknowledges mental disorders without granting complete exemption. India, however, lacks such intermediate doctrines, resulting in either complete acquittal under Section 22 BNS or full criminal liability.

In Ratan Lal v. State of Madhya Pradesh (2020), the Madhya Pradesh High Court noted that while neuro-scientific evidence may aid in understanding behaviour, the law still requires satisfaction of the McNaughten standard. This underscores the judiciary’s hesitancy to fully embrace neuro-legal innovations, perhaps due to concerns about reliability, standardisation, and misuse.

TOWARDS LEGAL REFORM: THE NEED FOR A NUANCED FRAMEWORK

The rigidity of the McNaughten rule and its codification under Section 22 BNS may no longer suffice in addressing contemporary scientific understandings of the human mind. Legal reforms should consider introducing the doctrine of “diminished responsibility,” which allows courts to impose reduced sentences where mental illness impairs judgment without completely eliminating culpability. This would balance individual justice with societal protection.

Furthermore, statutory recognition of neuro-legal evidence, coupled with judicial training on its interpretation, could enhance consistency. The Law Commission of India in its various reports has repeatedly stressed the need for modernisation of the insanity defence, yet legislative inertia persists. The new codes—BNS, BNSS, and BSA—though significant, have largely replicated colonial-era formulations, missing an opportunity to incorporate cutting-edge neuro-scientific developments.

The evolution of mental health and criminal responsibility in India reflects a complex interplay between legal traditions, constitutional mandates, and emerging scientific knowledge. While the BNS, BNSS, and BSA provide a restructured statutory framework, they continue to rely on the McNaughten rule, leaving little room for accommodating neuro-legal evidence. The future of criminal responsibility must move towards a more nuanced and humanised approach, recognising mental disorders not merely as absolute defences but as factors warranting differentiated treatment in culpability and sentencing. Only through such reforms can India ensure that its criminal justice system remains fair, humane, and scientifically informed.

—Vibha Rana is a final-year B.A.LL.B. student of Galgotias
University, Greater Noida

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