Four categories of brain function. The rating uses only one

Chapter 13 of the AMA Guides evaluates cerebral function across four domains.

AND THE GUIDES DIRECT THE EVALUATOR TO

“identify the most severe cerebral impairment from these four categories.” There may be impairment in all four. Only the highest rating from the most severe category is used.

Why the Guides do this is defensible: the four domains overlap heavily in their effect on daily function, and combining them would double-count the same disability. Why it produces unfair outcomes is also obvious: a person with four moderate deficits is more disabled than a person with one, and the method cannot see the difference.

The whole case becomes an argument about which category to rate under. That is not a technicality. It is where a brain injury case is actually won or lost, and it requires the evaluation to be built deliberately.

Consider a worker with documented memory and executive dysfunction on neuropsychological testing; emotional lability, irritability, and personality change reported by the family; a significant post-traumatic sleep disorder; and occasional word-finding difficulty.

The single highest-value action in a California brain injury case is making sure formal neuropsychological testing is completed, and that the evaluator has a detailed activities-of-daily-living history from someone who lives with the injured worker. Without those, the mental status category cannot be rated properly, and the case defaults to whatever was easiest to measure.

The four cerebral categories do not combine with each other. But brain injury frequently produces impairments outside Chapter 13’s cerebral section, and those do combine.

• Cranial nerve deficits — Loss of smell, loss of taste, visual field defects, facial numbness. Loss of the sense of smell after a head injury is a real, ratable impairment that is routinely never asked about. Neither is taste.
• Vestibular and balance disorders — Rated under the ear and equilibrium chapter.
• Post-traumatic epilepsy — Rated separately as an episodic disorder.
• Visual impairment — Rated under the vision chapter.
• Motor deficits from corticospinal tract damage — Routed through a separate table with its own axes — upper extremity function, station and gait, bladder, anorectal, sexual, and respiratory function — each with four classes keyed to activities-of-daily-living loss. The Guides use that approach specifically because “assessing ROM in paralyzed individuals is difficult.”
• Endocrine dysfunction from pituitary injury — Under-diagnosed after moderate-to-severe TBI. A pituitary panel is rarely ordered. These are small numbers individually and they combine.

The hardest cases in this area are the ones where imaging is normal. A concussion with a normal CTCT — Cumulative trauma Injury from repeated exposure over time. The largest injury category in California and the least claimed. and a normal MRI can still produce real, persistent, measurable cognitive impairment, and the defense position is predictable: no structural finding, no injury.

What answers it is testing, not argument. Formal neuropsychological testing with validity measures built in is the evidence that distinguishes a genuine mild TBI from a symptom report. Evaluators and judges take it seriously precisely because it includes internal checks on effort. What hurts these cases is the opposite: a six-month gap in treatment, no documented deficits close in time to the injury, and a first neuropsychological evaluation two years later. The record has to be built early.

And the co-occurring conditions matter. Post-traumatic headache, post-traumatic vestibular dysfunction, sleep disorder, and post-traumatic mood disorder are all common after mild TBI.

One trap specific to this injury. For injuries on or after January 1, 2013, the law bars an increase in the rating for “sleep dysfunction, sexual dysfunction, or psychiatric disorder” arising out of a compensable physical injury — all three, not just psychiatric. That matters here because the sleep and arousal disorders table sits inside the brain chapter’s first category. The counter-argument in a genuine brain injury case is that a post-traumatic arousal disorder is a direct neurological consequence of the brain injury itself rather than a “sleep dysfunction arising out of” it. The catastrophic-injury exception does not answer it: the law names “severe head injury” as a catastrophic injuryCatastrophic injury Under § 4660.1(c)(2)(B), “including, but not limited to, loss of a limb, paralysis, severe burn, or severe head injury.” Lifts the bar on psychiatric ratings., but the exception it creates is for a psychiatric disorder rating only. This has to be argued deliberately and supported in the medical report. It is not automatic.

That is the highest-stakes provision in a severe brain injury case. It is not a rating — it bypasses rating entirely. Where it applies, the worker is 100% permanently totally disabled as a matter of law, entitled to lifetime payment at the temporary disabilityTD / TTD / TPD Temporary Disability, Total or Partial. Wage replacement while recovering. Two-thirds of average weekly earnings; 2026 maximum $1,764.11/week. rate with annual cost-of-living increases.

It requires genuine permanent mental incapacity, and it is not available in most brain injury cases. In the cases where it is available, nothing else in the file matters as much.

LABOR CODE § 4662(a)(4)

Total disability is conclusively presumed from “an injury to the brain resulting in permanent mental incapacity.”

Expect: prior concussions, alcohol use, pre-existing psychiatric history, age-related cognitive decline, learning disability, and ADHD. Some of those have genuine literature behind them. The analysis does not change.

Apportionment is to permanent disabilityPD Permanent Disability. Compensation for lasting impairment. A different and much lower weekly rate — 2026 maximum $290/week., not to risk factors or history. Under EscobedoEscobedo The en banc decision requiring an apportionment opinion to explain how and why. A percentage without reasoning is not substantial evidence., the opinion must explain how and why the non-industrial factor caused a specific percentage of the disability. A physician who notes a college concussion and assigns 30% has stated a conclusion, not an opinion.

Where the mechanism was an assault, § 4660.1(c)(2)(A) applies independently — being the victim of a violent act permits the psychiatric rating regardless of whether the injury was catastrophic.