The new discovery:
[Some people trust their old beliefs more than the new information right in front of them, even when it clearly isn't working. Their decision becomes detached from reality. They cannot let go of an old belief even when the world has changed around them
Researchers at MIT have now identified the grin2a mutation as the reason.
It provides instructions for building part of the NMDA receptor, a protein on the surface of brain cells that is critical for learning, memory and adaptation.
When grin2a is mutated, that receptor doesn't work properly. Scientists call this 'NMDA receptor hypofunction,' or reduced function.
Researchers identified the mediodorsal thalamus as a key node in the broken circuit,
Our brain can form a prior belief of reality. When sensory input comes in, a neurotypical brain uses that new input to update the prior belief. That allows us to generate a new belief close to what reality is.
'What happens in some people is that they weigh too heavily on the prior belief. They don't use as much current input, so the new belief becomes detached from reality.'
Soon, internal thoughts and external reality begin to blur.]
This new discovery has effects on the choice to not think and to evade reality:
It can narrow, or even suspend, the scope of choice in the affected cognitive function; it does not, in principle, invalidate free will.
Reasoned analysis:
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What the study shows, in objective terms: Mutations that reduce GRIN2A-mediated NMDA receptor function impair a specific thalamo–prefrontal circuit (centered on the mediodorsal thalamus) needed for belief updating and cognitive flexibility. In mice, this yields perseveration; optogenetic activation of the circuit restores adaptive switching. That is causal, mechanistic evidence that part of “staying in touch with reality” depends on identifiable neural hardware.
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Objectivist principle: Consciousness has identity. Volition—the choice to focus—is not a mystic exception to causality; it is a capacity that functions by means of a specific organ with a specific mode of operation. If that organ is damaged or its chemistry is pathologically disrupted, the range within which choice can operate is reduced. The metaphysically given (biological impairment) cannot be wished away.
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Distinguishing evasion from impairment: Evasion is a willful refusal to focus in the face of facts when one is able to focus. The deficit identified here is an inability (in the affected circuit) to properly weight new sensory evidence against priors. When that inability is severe, the person’s failure to update beliefs is not a chosen rejection of reality but a causal malfunction. Moral judgment applies only to the extent of volitional control.
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Effect on “the choice to stay in touch with reality”: In normal functioning brains, staying in reality requires the active choice to focus, integrate new evidence, and revise conclusions. The study does not weaken this responsibility; it sharpens it by identifying the mechanism that implements evidence-weighting. In schizophrenia with NMDA hypofunction in the relevant circuit, the capacity to perform that integration is narrowed; in extreme cases it may be absent in that domain, suspending the applicability of “choice” there.
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Effect on “the choice to think or not”: The primary choice to focus remains the root of human cognition for those with the capacity to exercise it. In pathology, that choice can be partially available (varying by domain and severity) or, where the mechanism is nonfunctional, not available in that respect. Responsibility must be assessed contextually, in proportion to the intact scope of volitional control.
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Philosophical implications: The findings confirm the primacy of existence and causality. They neither support determinism of normal human action nor subjectivism; they delineate the boundary conditions of volition by identifying the biological means through which rational focus and evidence-integration occur.
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Practical corollaries consistent with Objectivism:
- Ethics: Judge by facts. Do not condemn as immoral what a person cannot control; do hold individuals responsible within the domains where their capacity to focus is intact.
- Law/policy: The state’s role is the protection of rights under objective law. Where objective medical evidence shows incapacity (non compos mentis), legal procedures should recognize diminished responsibility while aiming at treatment—not punishment for delusional error absent the initiation of force.
- Science/medicine: A rational path forward is to target NMDA receptor function and thalamo–prefrontal circuitry pharmacologically or via other objectively validated interventions. The study’s optogenetic rescue in mice is proof-of-concept for mechanism-based therapy, not a human treatment yet.
Bottom line: The discovery identifies a causal impairment of the neural means by which minds update beliefs. It restricts, and in severe cases suspends, the applicability of “choice” in that cognitive operation. It does not refute free will; it clarifies that volition operates only by a specific, biological faculty—one that can malfunction—and that moral judgment must be tied to the facts of a person’s actual capacity to focus.
In addition:
No clinical test can directly tell you whether GRIN2A-mediated NMDA receptor hypofunction is impairing the mediodorsal thalamus–prefrontal circuit in a living human today. Only indirect proxies exist, mostly in research settings.
What is available now (with limitations):
- Clinical genetic testing
- Targeted GRIN2A sequencing or broader panels (exome/genome) can identify variants.
- A variant is not proof of NMDA hypofunction in your thalamo–prefrontal circuit; functional impact is variant-specific and often uncertain. Penetrance is incomplete.
- EEG/MEG biomarkers linked to NMDA function
- Mismatch negativity (MMN), 40 Hz auditory steady-state response (ASSR), and P300. Schizophrenia cohorts often show reductions; these are consistent with NMDA receptor dysfunction but are not circuit-specific or diagnostic for the mediodorsal thalamus.
- Cognitive/neuropsychological tasks of flexibility/updating
- Probabilistic reversal learning, set-shifting (e.g., Wisconsin Card Sorting Test, IED), volatility learning paradigms with computational modeling. These can reveal belief-updating deficits but are not specific to GRIN2A or to the mediodorsal thalamus.
- MRI-based methods
- Resting-state/task fMRI to assess thalamo–prefrontal connectivity; diffusion MRI (DTI) for fronto-thalamic tracts. Findings can be abnormal at the group level in schizophrenia but are not validated as individual-level diagnostics.
- MR spectroscopy (MRS) to estimate glutamate/Glx in regions like anterior cingulate or thalamus. This is an indirect index; results are variable across studies and not specific to GRIN2A or to NMDA receptor channel function.
- PET imaging of NMDA receptors (research only)
- Tracers such as 18F-GE-179 or 11C-GMOM target open NMDA channels. Availability is limited to a few research centers; quantification and specificity remain under study.
- TMS-based physiology (mostly research)
- Paired associative stimulation, theta-burst stimulation, or TMS–EEG paradigms can probe NMDA-dependent plasticity; sometimes combined with pharmacological challenge (e.g., dextromethorphan/memantine). Not specific to the mediodorsal thalamus and not standard clinical diagnostics.
- Laboratory tests to exclude mimics
- CSF or serum anti–NMDA receptor antibodies (for autoimmune encephalitis) are clinically available but address a different disease mechanism than GRIN2A-related hypofunction in schizophrenia.
What this means in practice:
- There is no single “yes/no” clinical assay for GRIN2A-driven NMDA hypofunction in the mediodorsal thalamus–prefrontal circuit.
- Converging evidence can be assembled in specialized centers (genetics + EEG biomarkers + fMRI/MRS + cognitive testing), but interpretation remains probabilistic and research-grade.
If you want an objective workup:
- Start with a psychiatrist/neurologist to rule out reversible causes and establish diagnosis.
- If there is early onset, family history, or atypical features, request referral to clinical genetics for GRIN2A and related genes (with genetic counseling).
- Ask about participation in research protocols that include EEG (MMN/ASSR), fMRI/MRS, and, where available, NMDA PET or TMS–EEG. These are the closest current tools to probing the mechanism in vivo.
Principle: Volition operates by a specific biological faculty. If you want certainty, you must respect the limits of current measurement. Today’s science can indicate probability and mechanism; it cannot yet give a routine clinical readout of GRIN2A-mediated NMDA function in that specific thalamo–prefrontal circuit.
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