Grammar Processing by Sign Reflex: Neurobiological Adaptation in Quiet Environment

Native speakers acquire grammar effortlessly during early childhood, yet the neurobiological basis of this process remains poorly understood. While previous research has focused on cortical plasticity and innate syntactic modules—often proposed but not yet anatomically localized—few models have addressed the possibility that grammar may be implemented through reflex-based circuits at the subcortical level. Here we propose a neuro-immune hypothesis of grammar processing. According to this model, grammatical morphemes—typically monosyllabic—are encoded as phonological vectors and processed through brainstem auditory pathways that suppress spatial localization. These vectors are transmitted to cerebrospinal fluid-contacting neurons (CSF-cNs) on the ventricular walls, where motor proteins at the antigenic tips express phonological vector properties. B lymphocytes residing in the cerebrospinal fluid (CSF) recognize these vector-bearing antigens to instantly reconstruct meaning. This model distinguishes grammatical processing from lexical memory, which is formed through antigen-antibody specificity and B cell networking. Grammatical structures are decoded reflexively based on phonological vector patterns. The system is hypothesized to activate only under safe and quiet environmental conditions, allowing auditory resources to be reallocated from external vigilance to internal linguistic processing. The Amazonian Pirahã language, which lacks grammatical features such as tense, number, recursion, comparison, and logical connectives, offers a contrasting case. Pirahã speakers retain binaural hearing and maintain spatial awareness, suggesting that ecological factors can suppress grammar acquisition. We hypothesize that the unconscious acquisition of grammar is triggered by a genetically programmed postnatal switch, activated only under conditions of environmental safety and adequate stimulation. This model not only offers a biological explanation for grammar acquisition but also suggests a species-specific genomic adaptation unique to Homo sapiens.