Alzheimer’s is characterized by the accumulation of two specific "toxic" proteins that disrupt how neurons communicate.

• The Pathology: * Amyloid-β Plaques: These are hard protein clumps that build up between nerve cells, blocking the passage of signals at the synapses.

  • Tau Tangles: Inside the neurons, a protein called Tau collapses into twisted strands (tangles). This destroys the "transport system" that carries nutrients through the cell, eventually causing the neuron to die.

• Brain Region: Typically begins in the hippocampus, the brain's "filing cabinet" for new memories. This explains why short-term memory loss is usually the first clinical sign.

Unlike Alzheimer’s, which is driven by proteins, Vascular dementia is rooted in the brain’s blood supply.

• The Pathology: This occurs when blood flow to the brain is interrupted, often by a series of "mini-strokes" (TIA) or small vessel disease. When brain cells are deprived of oxygen and glucose, they suffer "infarction" (cell death).

• The "Step-wise" Progression: Scientifically, this often presents as a "step-wise" decline. Instead of a slow fade, a person may stay stable for months, then experience a sudden drop in cognitive ability following a small vascular event.

• Impact: It often affects the brain's white matter, which acts as the "wiring" connecting different regions. This is why "slowing of thought" and difficulty with planning are more common than simple forgetfulness.

DLB is closely related to Parkinson’s disease and involves the build up of a protein called alpha-synuclein.

• The Pathology: These protein deposits, called Lewy Bodies, develop in the areas of the brain responsible for thinking, visual perception, and muscle movement.
• The Scientific Hallmark: DLB is unique because it affects the autonomic nervous system. This explains why patients experience sudden drops in blood pressure, sleep disorders (acting out dreams), and "fluctuating cognition"—where a person may be perfectly lucid one hour and highly confused the next.

• Visual Perception: Because Lewy bodies often cluster in the visual cortex, "well-formed" hallucinations (seeing people or animals that aren't there) are a significant scientific marker.

FTD is a group of disorders caused by the progressive shrinking (atrophy) of the frontal and temporal lobes.

• The Pathology: FTD is often "young-onset," typically affecting people aged 45–65. It involves the loss of neurons in the areas of the brain that control executive function and social behaviour.

• Two Main Variants:

  • Behavioural Variant (bvFTD): Atrophy in the frontal lobe leads to a loss of "inhibition" and empathy. This isn't a "choice"; it is a physical inability of the brain to process social cues.

  • Language Variant (PPA): Atrophy in the temporal lobes destroys the "dictionary" of the brain, making it difficult to find words or understand their meaning.

• Genetic Factor: FTD has a stronger genetic link than other forms, with roughly 30-50% of cases having a family history.