Study on the Significance and Value of Interoception-Related Indicators in the Classification of Patients with Disorders of Consciousness (DoC) via Rectal Stimulation

Disorders of Consciousness (DoC) represent one of the sequelae of severe brain injuries caused by a variety of etiologies, including traumatic brain injury, stroke, and cardiac arrest. They may also result from primary neurological damage or systemic diseases. In recent years, with the advancement and development of surgical techniques and intensive care practices, an increasing number of DoC patients have survived life-threatening severe brain trauma. The large population of DoC patients imposes substantial psychological stress and economic burden on healthcare systems, social welfare services, and patients' families. Accurate identification and classification of DoC patients constitute a crucial prerequisite for clinical treatment and care.

Behavioral assessment of consciousness is currently the most common method for classifying DoC patients and is of great importance for critically ill patients. However, some cases of covert consciousness are difficult to identify, and even professional medical caregivers may encounter assessment errors. Such errors can lead to deviations in the selection of treatment strategies and the evaluation of prognostic efficacy for these patients. Precise diagnosis and classification of DoC are critical for prognostic treatment, as they enable the development of more rational rehabilitation protocols for patients and contribute to improving their quality of life.

The Coma Recovery Scale-Revised (CRS-R) is a standardized behavioral tool for the diagnosis of DoC. It primarily assesses patients' behavioral responses elicited by external sensory stimuli. The scale comprises six subscales: Auditory, Visual, Motor, Oromotor, Communication, and Arousal. Each subscale has a specific scoring range, with a total possible score of 23. Different total scores allow for the classification of patients into three categories: Vegetative State/Unresponsive Wakefulness Syndrome (VS/UWS), Minimally Conscious State (MCS, further divided into MCS+ and MCS-), and Emergent Minimally Conscious State (eMCS). However, the diagnosis and classification of VS/UWS and MCS using this scale are particularly challenging. This is because patients at the boundary between these two categories often exhibit highly similar behavioral responses to external stimuli, with only subtle differences. Additionally, the responses of DoC patients to behavioral assessments may be mere low-level reflexes or lack conscious involvement, making it difficult to achieve precise classification of DoC patients based solely on behavioral assessments.

Interoception refers to the bidirectional communication between the brain and the body's internal organs. Signals from internal organs-such as those related to heartbeat, respiratory movements, and gastrointestinal peristalsis-are transmitted to the cerebral cortex (including the insula and motor cortex) via the autonomic nervous system. Conversely, these cortical regions regulate the activity of target organs through the sympathetic and parasympathetic nervous systems. Interoception is essential for the maintenance of bodily homeostasis. Furthermore, a growing body of evidence indicates that interoception is also involved in higher cognitive functions, such as memory formation, emotional processing, and even the construction of the sense of self. Compared with exteroceptive pathways, the ascending interoceptive pathways in DoC patients tend to remain relatively intact. Therefore, interoception-related indicators, as a complement to exteroceptive behavioral response indicators, hold significant clinical value for the precise assessment of DoC patients.

Research on interoception-related indicators has emerged as a novel field for the differential diagnosis of DoC patients. These indicators serve as a vital supplement to behavioral and imaging assessments. Moreover, their application requires patients to engage in active conscious participation and induce awareness, which means interoception-related indicators can undertake the assessment tasks typically performed by imaging techniques in a more cost-effective and convenient manner. Consequently, they have inevitably become a focus of research in the field of consciousness and consciousness assessment.

Inclusion Criteria:

• Patients with non-acute Disorders of Consciousness (DoC) (disease course ≥ 28 days).
• Aged 18 years or older.
• No symptoms of fever, infection, or other similar conditions within 15 days.
• No use of sedatives within 15 days.
• No use of any drugs that may alter gastrointestinal motility within 7 days prior to testing.
• Family members of participating patients have provided consent and signed the informed consent form.

Exclusion Criteria:

• Patients with functional impairments caused by developmental psychiatric disorders or neurological diseases.
• Patients with untreated epilepsy.
• Untreated cerebral edema.
• Patients with unstable vital signs.
• A history of intestinal diseases.
• A history of abdominal surgery other than simple appendectomy or simple cholecystectomy.
• Organic diseases such as spinal cord injury, traumatic brain injury, and thyroid dysfunction.

Patients assessed as Minimally Conscious State plus/minus (MCS+/-) and Unresponsive Wakefulness Syndrome (UWS) using the Coma Recovery Scale-Revised (CRS-R)