Prevalent distribution of conscious processes on either side of the brain

Abstract

Objectives. The brain has an intrinsic tendency for the lateralization of its functions. For instance, the left hemisphere assists in the comprehension and motor expression of language. What remains uncertain is whether conscious processes are also more prevalent in one hemisphere of the brain than the other. The epistemic goal of this research was to address this particular issue. Materials and Methods. We observed the rare pathological event of proximal occlusion of the middle cerebral artery (MCA), which halts blood flow to the central two-thirds of a hemisphere, and examined its effects on consciousness. We aggregated individual scores for eyesopening and limb-motor responses from the Glasgow Coma Scale (GCS) to determine the conscious level, and used brain computed tomography imaging to identify the whole-territory infarcts of MCA. Results. Being a rare condition, we managed to recruit 35 patients from two centers (average age: 64.54 ± 13 years, 45.71% females). Whole-territory infarcts of the MCA occurred more frequently in the left hemisphere (22 versus 13, frequency: 62.85%). Unconsciousness was also more common with left hemisphere infarctions (16 versus 2 unconscious patients of the right hemisphere, Frequency: 72%, GCS: 2/10=3/22 cases, GCS: 5/10=1/22 cases, GCS: 6-7/10=12/22 cases). The difference in unconsciousness proved significant in Fisher’s exact analysis (p-value = 0.001) and remained independent of age (p-value=0.7247) and gender (p-value=0.3145). Moreover, six conscious patients with left hemisphere involvement exhibited a loss of conscious control for normal responses, implying a strong link between consciousness and cognition. Unconsciousness also correlated with stroke outcomes (16 Unconscious: 56.25% deceased within the hospital). Conclusion. Conscious processes are more predominant in the brain's left hemisphere. Our observations indicate that only a gross unilateral insult to the brain can lead to unconsciousness.

Keywords

• consciousness
• cognition
• infarction
• middle cerebral artery
• hemiplegia
• glasgow coma scale