Frontal lobe

Also known as: frontal lobes, frontal cortex, frontal lobe function

In one sentenceThe frontal lobe is the front part of each cerebral hemisphere. It controls voluntary movement, produces speech and, through the prefrontal cortex, plans and regulates behavior.

Location

The frontal lobe is the front portion of each of the brain’s two cerebral hemispheres, lying behind the forehead. A groove called the central sulcus separates it from the parietal lobe behind it, and another groove, the lateral sulcus, separates it from the temporal lobe below.

What the frontal lobe does

The frontal lobe is not a single unit. Different parts of it carry out different functions.

• Voluntary movement. The strip of cortex just in front of the central sulcus is the primary motor cortex, the main region responsible for voluntary movement. In 1937 Wilder Penfield and Edwin Boldrey mapped it in people with electrical stimulation and found that the body is laid out along it as an orderly map.
• Speech production. In 1861 the French surgeon Paul Broca described two patients who had lost the ability to speak after injury to the rear part of the inferior frontal gyrus. The region is now called Broca’s area.
• Executive functions. The frontal lobe is where much of planning, reasoning, problem solving and emotional regulation takes place. Research on these functions centers on its front-most part, the prefrontal cortex. Earl Miller and Jonathan Cohen proposed in 2001 that the prefrontal cortex keeps goals active and sends bias signals that steer activity in other brain regions toward the task at hand. It is also central to research on working memory.

Broca’s patients revisited

In 2007 Nina Dronkers and colleagues scanned the preserved brains of Broca’s two patients with high-resolution MRI. In both, the damage reached well into medial regions of the brain, beyond the surface lesions Broca had described. The area Broca originally identified also did not match exactly what is now called Broca’s area.

One lobe, several kinds of control

Damage to the frontal lobe has long been linked to problems with executive control, but lesion studies suggest this is not one ability. Reviewing patients with frontal lesions in 2007, Donald Stuss and Michael Alexander argued that executive function is a set of separate but interrelated attentional control processes rather than a single central executive. They described three, each tied roughly to a different area: energization (upper medial frontal cortex), task setting (left lateral) and monitoring (right lateral).

A 2010 study by Maria Roca, John Duncan and colleagues added a caution. On some widely used executive tests, such as Wisconsin Card Sorting, the poorer scores of patients with frontal lesions were entirely explained by lower fluid intelligence, the capacity for novel problem solving. Other tasks, including some cognitive and social tests, showed deficits that fluid intelligence did not fully explain.

Loops with deeper structures

Much of the frontal lobe works in loops with structures beneath the cortex. In 1986 Garrett Alexander, Mahlon DeLong and Peter Strick described parallel, functionally separate circuits that run from the cortex through the basal ganglia and thalamus and back to the frontal lobe. Dopamine neurons in the midbrain also send signals to the prefrontal cortex.

Is the human frontal lobe unusually large?

Humans’ distinctive cognitive abilities are often credited to a frontal lobe that grew disproportionately during evolution. In 2002 Katerina Semendeferi and colleagues compared MRI scans of living primates, including all the great apes, and found that human frontal cortex was not disproportionately large relative to theirs. They suggested that differences in individual cortical areas and richer interconnections may matter more than overall size.