Frontal lobe · Grey Matter

The frontal lobe is the front third of each hemisphere, the part of the cortex that turns goals into behaviour: it holds the plan, chooses among options, keeps impulses in check and finally sends the commands that move the body.

Frontal lobe. The frontal lobe is the front third of each hemisphere, the part of the cortex that turns goals into behaviour: it holds the plan, chooses among options, keeps impulses in check and finally sends the commands that move the body.

It reaches from the forehead back to the central sulcus, the deep groove that crosses the top of the hemisphere from side to side and separates it from the parietal lobe; the lateral fissure bounds it below, against the temporal lobe. Its work runs in a gradient from front to back. The prefrontal cortex at the front holds goals, rules and evaluation; the premotor areas behind it assemble sequences of movement; the motor cortex on the precentral gyrus, right in front of the central sulcus, sends the commands down to the spinal cord.

On the left side of most brains it also holds speech production. Broca's area lies on the inferior frontal gyrus, just in front of the motor areas for the mouth and larynx.

Damage shows as changes in behaviour more than in perception. A frontal lesion can leave sight, touch and memory intact while making a person impulsive, apathetic or unable to carry a plan through, depending on which part is hit.

The frontal lobe matures last. Myelination and synaptic pruning in the prefrontal part continue into the mid-twenties, after the sensory and motor areas.

Questions: What did the iron bar through Phineas Gage's frontal lobe change, and how much of the story is true? In 1848 a tamping iron about a metre long shot through the left cheek and out of the top of the head of a railway foreman, destroying much of the left frontal lobe, mainly its orbital and medial prefrontal parts and the white matter beneath. He survived, and his doctor reported that the efficient, well-liked man had become impulsive and profane. The historian Malcolm Macmillan later showed that many dramatic details were added by authors who never met him, and that Gage seems to have recovered substantially, later working for years as a stagecoach driver in Chile. The case still stands as early evidence that frontal damage can change judgement and social behaviour while leaving movement, speech and memory intact.