CorticalBrain.com
Home | NeuroAnatomy| Genetics| Neurology | Psychiatry| Psychology | Evolution | Functional Brain Mapping | Mail | Contact Us

The Brain's Cerebral Cortex (Neocortex)

Human Brain's Five Lobes


















The brain's frontal lobes:

Pyramidal Cell

The illustration to the left (image links to source) is a pyramidal cell, which is common in the prefrontal cortex. Bob Jacobs, Laboratory of Quantitative Neuromorphology, Department of Psychology, Colorado College, provides this photograph. In his video course, Sapolsky explains that the frontal cortex "helps you focus on what the task is right now. Early state dementia patients asked to count backward from 20 will start the task and then revert to reciting the months of the year. This dysfunction is called perseveration and intrusion—reverting to a previous task. Instead of doing the cognitively harder thing via the frontal cortex, the patient reverts to doing something over learned, remembered."

"The frontal cortex is involved in executive control, delayed gratification, long-term planning," writes Robert M. Sapolsky in Monkeyluv and Other Essays on Our Lives as Animals (2005). "It does this by sending inhibitory projections into the limbic system, a deeper, more ancient brain system involved in emotion and impulsivity. Furthermore, the frontal cortex excels at resisting stimulating inputs from the limbic system, ignoring tempting limbic whisperings like 'Screw the studying for the exam, run amok instead.'" Sapolsky later adds that when the frontal cortex is destroyed in a person, "you have a 'frontal' patient—sexually disinhibited, hyperaggressive, socially inappropriate. The frontal cortex is the closest thing we have to a neural basis for the superego."

Brain's Prefrontal Cortex

In this subsection, we discuss the frontal cortex generally. In the next subsection, we will discuss a particular portion of the frontal cortex, the orbital-frontal cortex, so labeled in the illustration to the right (links to source). In Part 2 of CorticalBrain.com, as part of a discussion of the VIGILANCE system, we discuss Stress, attention, learning, and memory, including the effects of stress on neurocircuitry in what is called the prefrontal cortex, a larger area also illustrated in the image to the right (links to source).

Temple Grandin and Catherine Johnson make a good point in Animals in Translation: Using the Mysteries of Autism to Decode Animal Behavior (2005). If you damage any part of your brain in an accident or a stroke, they explain, it may appear that you have damage to your frontal lobes, even when your frontal lobes remain perfectly intact. "People always thought this was because the last structure to evolve is the most delicate, while the older structures have been around so long they've become incredibly robust. But a neuropsychologist named Elkhonon Goldberg at New York University School of Medicine, who wrote a fantastic book about frontal lobe functions called The Executive Brain, has a different theory. He thinks that while the frontal lobes may be more fragile, there is another factor involved, which is that every other part of the brain is connected to them. When you damage any part of the brain, you change input to the frontal lobes, and when you change input, you change output. If the frontal lobes aren't getting the right input, they don't produce the right output even though structurally they're fine. So all brain damage ends up looking like frontal lobe damage, whether the frontal lobes were injured or not."

The orbital-frontal cortex and Phineas Gage:

Brain's Orbital Frontal Cortex

"In primates, the frontal lobe has an important role in establishing priorities and planning," writes Allman in Evolving Brains. "In particular, the lower surface of the frontal lobe, termed the orbital-frontal cortex, is especially important for these functions, as has been shown by an extraordinary series of clinical observations of brain-damaged patients by Antonio Damasio and his team in the Department of Neurology at the University of Iowa College of Medicine."

the term orbital-frontal cortex is used consistently in this narrative. The location of this most important region is highlighted in the image above right (links to source; this image is an MRI of Wikipedia contributor Paul Wicks's brain). In reading, however, you are likely to come across other terminology that designates areas of the brain slightly different from that pictured above. Damasio, for example, clarifies his use of terms in Descartes' Error: "In neuroanatomical terminology, the orbital region is known also as the ventromedial region of the frontal lobe, and this is how it is referred to throughout the book. 'Ventral' and 'ventro-' come from venter, 'belly' in Latin, and this region is the underbelly of the frontal lobe, so to speak; 'medial' designates proximity to the midline or the inside surface of a structure."

Brain's Sylvian Fissure

The importance of the brain—especially frontal regions of the neocortex—in shaping behavior and personality began to be realized in the aftermath of an astonishing injury to a man named Phineas Gage in 1848, then a reliable and successful construction foreman working on the railroad in Vermont. Gage was using a tamping iron to compact material—including explosive powder that at some point in time is topped with sand—into a hole drilled into a bed of rock when he accidentally set off an explosion that sent a tamping iron through his head. (Beverly and Jack Wilgus own the original daguerreotype of Gage, pictured at left holding the tamping iron that shot through his head. The image links to their web site, Meet Phineas Gage.) Although Gage was not able to return to work as a foreman, he did pursue and obtain other employment relating to the care and management of horses. After learning something about brain evolution and ethology, in this subsequent work Gage engaged with animals. But before we get to this topic, lets review a few facts about the accident and Gage's medical treatment, taken from the well researched An Odd Kind of Fame: Stories of Phineas Gage (2002), by Malcolm Macmillan.

Macmillan provides all the unpleasant but extremely interesting details of how physician John Martyn Harlow treated Gage's injury. These details include the following: "During his 1848 examination he [Harlow] had explored the wound by placing one index finger in the opening in the skull until it 'received the other finger in like manner' from the wound in the cheek."

Macmillan explains that the tamping iron "was three feet and seven inches long, one and one-quarter inches in diameter at the larger end, tapering over a distance of about twelve inches to a diameter of one-quarter of an inch at the other, and weighed thirteen and one-quarter pounds."

Macmillan presents two versions of the accident—one from Harlow, who tended to Gage's wound and thus saved his life, and the other from Henry Jacob Bigelow, who presented Gage and his tamping iron at an 1849 meeting of the Boston Society of Medical Improvement. It should be noted here that Macmillan favors Harlow's version. Macmillan writes:

According to Harlow, Gage was tamping the powder and fuse ("slightly" in the 1848 account) prior to the sand's being poured in when his attention was attracted by his men, who were loading excavated rock onto a platform car in the pit a few feet behind him. With his head still averted and while continuing to look over his right shoulder, Gage dropped the iron onto the powder again where, this time, it hit the rock, struck a spark, ignited the charge, and immediately reversed its initial direction. Bigelow had it differently. According to Bigelow, the powder and fuse had already been "adjusted" in the hole, and Gage had instructed an assistant to pour in the sand. While waiting for this to be done, Gage turned his head away, and after an interval of a few seconds again dropped the iron, this time, as he supposed, onto the sand. However, no sand had been added, and, when the bar struck the rock, the charge exploded, driving it upward.

In terms of his occupation before the accident, Harlow described Gage as a "businessman." Macmillan explains that in 1848, the term "businessman" was used primarily to describe "one who organized the work of others." Macmillan points out that the most reliable evidence we have about Gage before the accident is that he was a "foreman of a gang of men constructing the bed for the railroad." In his job as foreman, Gage "had to allot tasks to the men in his gang fairly, record accurately the time each man spent on each task, treat the men comprising the gang equally, and pay them properly." After the accident, however, Macmillan reports that when Gage felt well enough to return to work, his employers "would not give him his position back" because the "damage to his brain had changed him too profoundly."

During Gage's recovery period, Macmillan details how Harlow began to notice unusual behavior. Regarding his patient, Harlow wrote: "Does not estimate size or money accurately, though he has memory as perfect as ever. He would not take $1,000 for a few pebbles which he took from an ancient river bed where he was at work." In several references to the recovering Gage, Harlow described his patient as "very childish."

Macmillan explains that what we know of Gage's employment subsequent to the accident comes from Harlow. After spending some time displaying his injury and tamping iron in a museum setting, Harlow wrote that Gage began working with horses. In 1851, Gage "engaged with Mr. Jonathan Currier, of Hanover [New Hampshire], to work in his livery stable." From Harlow we also know that Gage "remained there without any interruption from ill health for nearly or quite a year and a half." Macmillan writes: "We may presume he looked after the horses and that he also drove coaches."

The gold rush and its associated influx of people into California, explains Macmillan, may be responsible for what Gage did in 1852. Harlow wrote that Gage "engaged with a man who was going to Chili, in South America, to establish a line of coaches at Valparaiso." Macmillan writes: "In the 1850s Valparaiso was popular as a first port of call on the western seaboard for ships from the eastern United States going to California via South America. As supplies were being replenished, passengers would take a few days' rest, during which time they often traveled the approximately seventy-five miles to the Chilean capital, Santiago." Harlow wrote that Gage was "occupied in caring for horses, and often driving a coach heavily laden and drawn by six horses."

In detailing how the Gage case shaped thinking about localization of brain function, Macmillan calls attention to the work of David Ferrier (1843-1928). Ferrier's work with monkeys demonstrated that "frontal ablation in the monkey produced behavioral changes that Ferrier came to consider as being exemplified by Gage and that could be explained by the loss of a frontally localized inhibitory-motor function." Ferrier reported that the loss of that function caused, "a form of mental degradation, which may be reduced in ultimate analysis to the loss of the faculty of attention."

Macmillan reports that in 1884, 36 years after Gage's injury, M. Allen Starr published "the first modern comparison of the effects of different kinds of [brain] lesions and tumor" and that Gage figured prominently in the report. Macmillan proposes that Starr also drew on Ferrier's "inhibitory" thesis. Macmillan includes the following from Starr's published comparison:

The mind exercises a constant inhibitory influence upon all action, physical or mental; from the simple restraint upon the lower reflexes, such as the action of the sphincters, to the higher control over the complex reflexes, such as emotional impulses and their manifestation in speech and expression. This action of control implies a recognition of the import of an act in connection with other acts; in a word, it involves judgment and reason, the highest mental qualities. By inhibiting all but one set of impulses it enables one to fix attention upon a subject, and hold it there.

In the twenty-first century, we better understand that the role of specialized areas of the neocortex—the frontal lobes especially including the orbital-frontal cortex—is to modulate or "inhibit" emotion-driven behavior originating in subcortical mammalian brain structures. We share subcortical structures with all mammals including horses. Under optimal circumstances, our large human fontal lobes inspire us to adjust behavior based on environmental circumstances as well as familial, cultural, and societal influences. Although we can survive without certain components of the neocortex, we are subsequently very different in terms of personality, temperament, and judgement. We discuss the emotional systems based in subcortical structures in detail in Part 2 of CorticalBrain.com


Next-> The Brain Cerebral Cortex Neocortex - The brain's frontal lobes

To continue exploring CorticalBrain.com in an orderly fashion, link to Subcortical Brain Structures, Stress, Emotions, and Mental Illness. Or, you may Explore the Site Outline.

If you would like be informed about new features and improvements as they are added to CorticalBrain.com, please send an e-mail to info(at)corticalbrain.com