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Could the Brain’s Physical Shape Help Explain Why Alzheimer’s Attacks Certain Memory Regions First?
Guest Contributor
Alzheimer’s disease has long been framed around toxic proteins and failing neurons, yet a new line of research invites people to look at something far more basic: the physical shape of the head and how the brain sits inside it. Neuroscientists are beginning to ask whether subtle pressure points created by everyday movement and the steady pull of gravity might influence where Alzheimer’s disease begins. This unusual focus on head shape, the tentorial notch and “selective vulnerability” could add a fresh dimension to how researchers understand neurodegeneration.
For decades, one of the deepest puzzles in brain science has centered on why certain regions are hit hard by disease while others remain relatively spared. This pattern, called selective vulnerability, is especially visible in Alzheimer’s. Long before memory problems become obvious, tangles of a protein known as tau begin to accumulate in a small region near the base of the brain called the entorhinal cortex. Cells in this area die first and the damage then spreads outward. The question that has unsettled researchers is why this region is the starting point at all.
In a preliminary study, scientists noticed that tau buildup in this early “ground zero” region seemed linked to the course of Alzheimer’s only when one other factor was present. The entorhinal cortex had to sit very close to the edge of a structure called the tentorial incisura, a notch in the brain’s tough outer covering. That detail raised a provocative possibility. Could repeated, tiny mechanical stresses where brain tissue meets a rigid edge increase the risk that tau pathology turns into full Alzheimer’s disease?
From that question flows a cascade of others. If everyday movement and the long-term slouch of gravity concentrate strain along certain borders inside the skull, perhaps those borders become biological weak spots. Could that biomechanical wear and tear influence who develops dementia and who does not? And if so, might individual differences in skull shape and brain positioning quietly shift risk over a lifetime?
This line of thought has been discussed carefully in scientific circles in part because it brushes against a troubling historical legacy. In the 19th century, pseudosciences such as phrenology used head shape to make unfounded claims about personality and to justify discrimination and racism. Modern researchers are clear that their work is grounded in neurology and biomechanics, not in personality prediction or social judgment. Outside scientists who reviewed the study called the idea intriguing, while emphasizing that the evidence is preliminary and must be rigorously tested.
The recent study grew out of work by Dr. John Crary, a neuropathologist at the Icahn School of Medicine at Mount Sinai, and Frank Provenzano, a neural imaging bioengineer at Columbia University. Crary directs a brain bank and has spent years examining the ways physical forces affect neural tissue. He previously studied chronic traumatic encephalopathy, or CTE, a degenerative brain condition seen in people with repeated head trauma. CTE has already shown that mechanical forces can contribute to the accumulation of harmful tau tangles.
Crary’s curiosity about anatomy and mechanical stress deepened when he encountered a 1958 paper that documented an unusual autopsy technique. In that work, a portion of the skull was removed in a way that exposed a central opening in the brain coverings called the tentorial notch. The paper reported that this notch varied widely among individuals. Some were large, others small; some longer, others shorter. Crary wondered whether these natural variations might translate into different patterns of pressure when the brain moves slightly inside the skull every time a person walks, turns or nods.
In acute situations, such as severe head injury or stroke, physicians already know that swelling brain tissue can press dangerously against the tentorial edge. Crary began to speculate about whether smaller, chronic forces might also matter in slower diseases such as Alzheimer’s. If a person’s entorhinal cortex lies very close to the hard rim of the tentorial notch, perhaps that proximity, combined with lifelong motion, could help explain why this region appears so vulnerable.
To explore this idea, Crary and Provenzano analyzed brain scans from 47 people with mild cognitive impairment who already showed tau accumulation in the entorhinal cortex. They measured the distance between the outer edge of the tentorial notch and this tau-prone brain structure. On its own, the distance did not predict how much tau had accumulated. Nor did head and brain architecture by themselves identify who would definitely go on to develop Alzheimer’s disease.
The compelling result appeared when they combined observations. Among people whose entorhinal cortex sat close to the tentorial notch, tau accumulation in that region was associated with a higher likelihood of progressing to dementia over the following three years. In contrast, when there was a larger gap between the cortex and the notch, the same regional tau burden was not as clearly linked to subsequent Alzheimer’s diagnosis. The authors interpreted this pattern as an “intriguing correlation” rather than proof of cause and effect. It was a signal that anatomy might modulate the impact of existing pathology.
Researchers who were not involved in the study welcomed the work as a creative contribution to Alzheimer’s research, while stressing the need for much larger and more diverse samples. Some pointed out that the distance between the entorhinal cortex and the tentorial notch might correlate with other biological or developmental factors that could also influence dementia risk. Others highlighted plausible biological mechanisms. Microglia, the immune cells that help clear amyloid beta from the brain, are known to be sensitive to stretching and mechanical stress. Changes in their behavior around a pressure point could, in theory, alter how toxic proteins are handled.
Even critics of the study’s limitations tended to support one central message. The field has concentrated heavily on amyloid plaques and tau tangles for over a century. While that work remains essential, it may not fully explain why some people with a high protein burden stay cognitively healthy, while others decline quickly. Considering how brain tissue is shaped, supported and strained inside the skull might add an important new dimension.
Other recent work hints that the “slouch of gravity” over time can reshape the aging brain. Researchers at the University of California, Irvine, for example, tracked how brain structures compress in some directions and stretch in others as people grow older. They found that certain aspects of this subtle remodeling were more pronounced in older adults experiencing memory and thinking problems. These findings align with the idea that gentle but persistent mechanical forces are part of the broader story of cognitive aging.
The emerging conversation around head shape and Alzheimer’s risk is not about predicting a person’s future from the outline of their skull. It is about acknowledging that the brain is not floating in a vacuum. It sits in a physical container, held by membranes and surrounded by bone. As people move through the world and live longer lives, those structures interact in complex ways. Understanding these interactions could eventually help explain why specific regions are so fragile and, perhaps, reveal new ways to protect them.
Many questions remain open. Do these anatomical features matter in other neurodegenerative diseases beyond Alzheimer’s and CTE? Could imaging techniques one day incorporate measurements of mechanical risk alongside traditional biomarkers? The current study does not yet offer clinical answers, but it does invite scientists to widen their lens. By paying attention to how structure, motion and biology intersect, researchers may uncover fresh paths toward prevention and treatment, even if the initial hypotheses evolve or prove incomplete.