The cortex is the external surface of the brain. Fleischman describes it as being closely related to thought, memory, language, imagination, sensation, and emotions. While 19th-century physicians understood the large structures of the brain, they didn’t understand how the cortex operates, nor were they aware of how the various parts of the cortex are organized. Gage’s injury damaged a region within the anterior (frontal) part of the cortex. His case is central to how the brain operates and where portions of mental functions are located.

Executive functions are cognitive processes associated with the frontal cortex that enable individuals to evaluate the consequences of actions and plan future activities. Executive functions, Fleischman says, explain why Gage demonstrated continued physical capabilities and intellectual competence, albeit in limited ways, while continuing to be significantly impaired in judgment, emotional responsiveness, and social interactions. Gage’s injuries disrupted certain mental processes that facilitated interaction among humans and the ability to make decisions and plan.

The frontal lobe refers to the anterior (frontal) segment of the cortex located in close proximity to the eyes. It is made up of left and right sections, or lobes. Fleischman describes how the tamping iron entered Gage’s frontal lobe without damaging motor functions, sensory reception, or speech production. The frontal lobe is the foundation for understanding Gage’s personality changes and impaired judgment. Human decision-making and sociability are correlated with this brain area.

Germ theory developed during the 18th and19th centuries. It defines microorganisms as causative agents for infectious diseases. Scientists had identified microorganisms under microscopes and established their existence as entities separate from normal cells well before 1848, the year Gage was injured. However, no physician at that time recognized that microorganisms cause infections and diseases. Germ theory illustrates the dangers associated with Gage’s wound—and the improbability of his survival. Despite having a tamping iron lodged in his brain and living in a period before sterile technique and antibiotics, Gage survived.

Phrenology was a scientific theory of the 19th century. It suggested that specific organs of the brain are responsible for controlling distinct aspects of one’s mind and morals. Phrenologists claimed that specific features on an individual’s cranium represent areas of organ development and reflect an individual’s mental characteristics and/or moral values.

Fleischman treats phrenology as a historical precursor to contemporary neuroscience. He says that it provided some insights into how brains operate but ultimately utilized flawed methodologies and drew incorrect conclusions. Phrenology demonstrates how early attempts at understanding how brains operate combined valid ideas with speculative notions. In addition, phrenology illustrates how Gage’s case became involved in competing theories attempting to explain how minds function.