Removing the frontal lobe disrupts an unusually wide range of abilities, from planning and impulse control to language, motor coordination, smell, and even the capacity for moral reasoning. Because the frontal lobe is the brain’s largest region and sits at the crossroads of almost every major cognitive network, no other single-lobe removal produces such sweeping changes. The specific deficits depend on which subregions are lost and whether the damage is one-sided or bilateral, and the picture gets more complicated still when you factor in the person’s age and how much tissue is actually taken.
Why the Frontal Lobe Matters So Much
The frontal lobe takes up roughly a third of the brain’s surface area. It houses the primary motor cortex (which controls voluntary movement on the opposite side of the body), Broca’s area (critical for producing speech), the prefrontal cortex (the seat of planning, working memory, and abstract reasoning), and several specialized zones for eye movement, smell processing, and social behavior. The human prefrontal cortex has expanded dramatically compared to that of other primates, particularly its most anterior portion, the frontopolar cortex. That expansion is tied to three broad cognitive advances: a larger working memory capacity for integrating past and future, a greater ability to link distant or unrelated pieces of information, and an enhanced capacity for abstraction, including analogical reasoning and the formation of moral beliefs.1PubMed Central. The prefrontal cortex: from monkey to man Losing the frontal lobe, in other words, strips away the hardware behind many of the traits people think of as uniquely human.
Personality and Behavioral Changes
The earliest and most famous illustration of frontal lobe damage is Phineas Gage, the railroad worker who survived an iron rod blasting through his skull in 1848. His case was perhaps the first to demonstrate that specific brain areas shape personality and that damage to them produces specific mental changes.2PubMed Central. Phineas Gage’s great legacy Gage reportedly shifted from being reliable and socially appropriate to impulsive, profane, and unable to stick with plans. That pattern turned out to be remarkably consistent across later clinical observations.
The most systematic data comes from the era of prefrontal lobotomy, when surgeons deliberately severed frontal connections to treat psychiatric illness. A follow-up study of lobotomy patients roughly a decade after surgery found that a personality defect was the single most common complication, appearing in about 91% of patients. Epilepsy was the next most frequent problem, occurring in about 12%.3PubMed Central. The lobotomy patient–a decade later: a follow-up study of a research project started in 1948 “Personality defect” in this context typically meant blunted emotions, social inappropriateness, a loss of initiative, or some combination of all three. These patients could often hold a conversation and perform simple tasks, but the person they had been before surgery was, in a meaningful sense, gone.
Executive Function and Intelligence
The dorsolateral prefrontal cortex, a region on the outer upper surface of the frontal lobe, plays a central role in general intelligence and executive function. Patients with focal damage to this area score lower on both latent measures of general intelligence and individual tests of executive ability, including planning, set-shifting, and problem-solving.4PubMed Central. Dorsolateral prefrontal contributions to human intelligence The research on this area is striking for an additional reason: when the influence of general intelligence was statistically removed, the specific executive deficits were no longer significant on their own. That suggests the dorsolateral prefrontal cortex is not just running a few isolated executive tasks; it is a hub supporting the broad cognitive capacity that underlies many different mental abilities at once.
A separate study following adults who had undergone frontal lobectomy for drug-resistant epilepsy found that about half showed no meaningful decline in cognition after surgery. An additional 42% showed decline in just one or two cognitive domains, most often intelligence scores, visuomotor processing speed, or executive functioning.5PubMed Central. Neuropsychological outcome following frontal lobectomy for pharmacoresistant epilepsy in adults That might sound surprisingly mild, but these were carefully planned partial removals that spared motor and language areas. A complete frontal lobe removal would be far more devastating.
Impulse Control and Risky Decision-Making
The lower and inner surfaces of the frontal lobe, especially the orbitofrontal cortex, are where the brain evaluates rewards, weighs consequences, and adjusts behavior when something goes wrong. Damage here does not simply make people impulsive in a generic, “can’t sit still” way. Research on patients with frontal lobe lesions has drawn a useful distinction between impulsivity and risk-taking. Impulsivity, the tendency to respond before thinking, was linked to various frontal sites. But risk-taking, the tendency to choose options with poor odds even when the stakes are clear, was specifically tied to damage in the left ventrolateral and orbital regions. These patients also showed blunted reactions after a choice failed to pay off, meaning they did not adjust their strategy the way a healthy person would.6PubMed. Impulsivity and risk-taking behavior in focal frontal lobe lesions
A complementary study focused specifically on orbitofrontal cortex patients confirmed that they scored as more impulsive on both self-report questionnaires and cognitive tests, reported more socially inappropriate “frontal” behaviors, and performed worse on tasks requiring them to reverse learned associations between a stimulus and a reward.7PubMed. Impulsivity, time perception, emotion and reinforcement sensitivity in patients with orbitofrontal cortex lesions In everyday terms, these are people who struggle not just to resist temptation but to learn from negative outcomes at all. They keep choosing badly because the emotional signal that should flag a bad decision is weakened or absent.
Social Cognition and Moral Reasoning
A less obvious but equally important role of the frontal lobe involves understanding other people. The ventromedial prefrontal cortex contributes to recognizing emotions in faces, reasoning about what other people are thinking, and processing information about oneself. It performs these tasks through connections with the posterior cingulate cortex, the precuneus, and the amygdala, among other structures.8PubMed Central. The Multifaceted Role of the Ventromedial Prefrontal Cortex in Emotion, Decision Making, Social Cognition, and Psychopathology Losing this region makes social life profoundly difficult, not because patients become intellectually incapable, but because they lose the intuitive emotional compass that guides social interaction.
This shows up in moral reasoning as well. In one study, patients with ventromedial prefrontal damage were more willing to judge personal moral violations as acceptable, and they reached those judgments faster than healthy controls. When faced with impersonal moral dilemmas or non-moral decisions, their performance was normal.9PubMed Central. Selective deficit in personal moral judgment following damage to ventromedial prefrontal cortex The implication is that this region generates the anticipatory emotional reaction, the gut feeling that harming someone is wrong, which shapes moral choices. Without it, people can still reason abstractly about ethics, but the visceral brake that prevents harmful decisions in the heat of the moment is weakened.
Language and Speech Production
Broca’s area, located in the left inferior frontal gyrus for most people, has been linked to speech production since the 1860s. The relationship between this region and aphasia is real but more nuanced than textbooks suggest. A large study of 289 neurosurgical patients found that postoperative Broca’s aphasia was most strongly associated not with the classic Broca’s area itself, but with an overlapping zone spanning the ventral sensorimotor cortex, supramarginal gyri, and underlying white matter tracts.10Journal of Neurosurgery. Dissociation of Broca’s area from Broca’s aphasia in patients undergoing neurosurgical resections That means a surgeon can sometimes remove tissue within the traditional boundaries of Broca’s area without causing permanent aphasia, while damage to adjacent structures may produce severe speech deficits.
Still, frontal lobe resection near language zones carries real risks. In one case, a patient who underwent removal of part of the right inferior frontal lobe for epilepsy was initially mute after surgery. After a month of intensive speech therapy, muteness gave way to aphasic speech, and over the next year the patient gradually recovered, though mild word-finding difficulties and speech slowness persisted.11Epilepsy & Behavior Case Reports. Language recovery after epilepsy surgery of the Broca’s area That trajectory, an initial devastating loss followed by slow partial recovery, is common after frontal language-area resections.
Motor Control and Eye Movements
The frontal lobe contains the primary motor cortex, which runs along the precentral gyrus and controls voluntary movement on the opposite side of the body. Damage to this strip classically causes weakness or paralysis on the contralateral side, but recent work has shown that deficits can appear in both upper limbs, not just the one opposite the lesion.12PubMed Central. Volumetric effects of motor cortex injury on recovery of ipsilesional dexterous movements Fine dexterity, in particular, seems vulnerable even on the same side as the damage. Modern epilepsy surgery goes to great lengths to spare the primary motor cortex and premotor areas, mapping them in advance so that tissue removal stays within “non-eloquent” zones.13PubMed Central. Surgical Technique and Outcome of Extensive Frontal Lobectomy for Treatment of Intracable Non-lesional Frontal Lobe Epilepsy
The frontal eye fields, located in the posterior part of the frontal lobe, coordinate voluntary eye movements. When one frontal eye field is damaged, the effects can be subtle but measurable. A case report documented a patient with a damaged right frontal eye field who almost entirely lost the ability to make vertical saccades, the quick eye jumps used to scan a scene, during visual exploration.14PubMed Central. Loss of exploratory vertical saccades after unilateral frontal eye field damage Losing both frontal eye fields would likely make scanning a visual environment extremely difficult, affecting everything from reading to navigating a busy room.
Smell, Motivation, and Autonomic Function
The orbitofrontal cortex sits directly above the nasal cavity and is the primary cortical region for processing smell. Damage here can cause lasting anosmia, the inability to identify or distinguish odors. In one case, a patient with traumatic brain injury and post-traumatic scarring in the right orbitofrontal cortex showed a marked decrease in the ability to identify and discriminate odors, even though the basic ability to perceive that an odor was present remained largely intact.15PubMed. Persistent anosmia in a traumatic brain injury patient: role of orbitofrontal cortex People with this kind of deficit can tell that something smells, but cannot tell you whether it is coffee or gasoline.
The frontal lobe also houses circuits critical for motivation and spontaneous behavior. The anterior cingulate cortex, tucked along the inner surface, is a key node in the motivation network. Damage here, or disruption of its connections, can produce abulia, a state characterized by profound apathy and a near-total absence of self-initiated action. A person with abulia might sit motionless for hours, not because they are paralyzed or depressed in the usual sense, but because the neural drive to initiate behavior has been disconnected.16NeuroImage: Clinical. The circuitry of abulia: Insights from functional connectivity MRI
How Much Gets Removed Matters Enormously
A complete frontal lobectomy, removing the entire lobe on one or both sides, would produce a combination of all the deficits described above. In practice, modern neurosurgery almost never does this. When frontal tissue is removed today, it is typically a partial resection for drug-resistant epilepsy or a tumor, with careful preoperative mapping to preserve motor cortex, language areas, and as much prefrontal tissue as possible.
Even extensive frontal lobectomy for epilepsy aims to maximize removal of gray matter in non-critical zones, including the orbital gyrus and subcallosal area, while sparing the primary motor cortex, premotor cortex, and certain deep structures.13PubMed Central. Surgical Technique and Outcome of Extensive Frontal Lobectomy for Treatment of Intracable Non-lesional Frontal Lobe Epilepsy Pre-surgical imaging with functional MRI and white-matter tract mapping has improved outcomes: patients who receive this kind of detailed mapping before surgery are more likely to preserve or improve their neurological function afterward.17PubMed Central. Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging-Tractography in Resective Brain Surgery: Lesion Coverage Strategies and Patient Outcomes
An interesting wrinkle from the lobotomy literature complicates the picture. A study of schizophrenic patients examined roughly 25 years after prefrontal leukotomy found that those with larger frontal lesions, particularly asymmetric ones, actually had better psychiatric outcomes and better psychological test performance than those with smaller lesions.18PubMed. The long-term effects of prefrontal leukotomy That does not mean removing more frontal lobe is better in general. It reflects the specific context of severe schizophrenia, where the diseased tissue may have been causing more harm than its absence. The principle holds, though, that the consequences of frontal removal depend not just on how much tissue is lost but on what condition the tissue was in to begin with.
Visual Short-Term Memory
One consequence of frontal lobe removal that rarely makes headlines is a reduction in visual short-term memory. Research comparing patients who had undergone right frontal-lobe excisions with control groups found that the frontal patients showed impaired visual pattern span across all testing conditions, whether distractions were present or not. The deficit appeared to stem from a decreased ability to encode complex visual patterns under time pressure.19Neuropsychologia. Capacity of visual short-term memory after unilateral frontal or anterior temporal-lobe resection This kind of impairment does not show up on standard intelligence tests but affects practical tasks like reading a map, following a recipe with multiple steps, or keeping track of objects in a cluttered environment.
Recovery and the Advantage of Youth
The brain’s ability to compensate after frontal lobe removal is real but limited, and age is the single biggest factor. Children who undergo frontal lobe surgery for low-grade tumors show a remarkable pattern of recovery. Functional connectivity between frontal regions and deep brain structures drops immediately after surgery, as you would expect, but then rebounds within months as the brain reorganizes its networks.20PubMed Central. Early recovery of cognition and brain plasticity after surgery in children with low-grade frontal lobe tumors The developing brain has a plasticity that the adult brain largely lacks, and children can sometimes shift functions to adjacent regions or even to the opposite hemisphere in ways that would not happen in a 50-year-old.
Adults do recover, but more modestly. In the frontal lobectomy study for epilepsy cited earlier, older age at the time of surgery was one of the factors associated with cognitive decline on some measures.5PubMed Central. Neuropsychological outcome following frontal lobectomy for pharmacoresistant epilepsy in adults Higher preoperative ability was also a risk factor for decline, likely because people starting at a higher cognitive baseline have more room to fall. The absence of a structural brain abnormality on MRI and poor seizure control after surgery were also linked to worse cognitive outcomes.
What Rehabilitation Looks Like
Rehabilitation after frontal lobe damage focuses on the deficits that matter most in daily life, primarily problem-solving, planning, and social behavior. One approach uses simulation-based training: patients practice making decisions in realistic scenarios while a therapist guides them through recognizing errors and adjusting strategies. A case study of a patient with traumatic frontal lobe injury found that targeted cognitive training using decision-making and problem-solving vignettes produced significant improvements in executive cognitive-behavioral areas within three months.21PubMed. Simulation-based executive cognitive assessment and rehabilitation after traumatic frontal lobe injury: a case report The first stage of that program focused on building the patient’s awareness of their own deficits, a step that is itself frontal-lobe-dependent and often the hardest to achieve.
Speech therapy, occupational therapy, and behavioral management programs form the rest of the rehabilitation toolkit. The common thread is compensation rather than restoration. A patient who has lost the ability to plan ahead might learn to use external tools, like checklists, phone alarms, or structured daily routines, to substitute for the internal planning capacity that is no longer reliable. The brain may not regrow the lost tissue, but with sustained effort, many patients can build scaffolding around the gaps.
Why This Is Not a Clean Subtraction
One persistent misconception is that removing a brain region simply “subtracts” the abilities it handles, leaving everything else untouched. The frontal lobe is deeply connected to nearly every other brain region, so removing it disrupts networks that extend far beyond the tissue that was actually taken out. The motivation circuit is a good example: abulia can result from damage to the anterior cingulate cortex, but also from damage to distant structures like the striatum or thalamus, because they share a functional network. When frontal lobe tissue is removed, the downstream effects on connected regions can produce symptoms that seem to have nothing to do with the frontal lobe itself, including memory problems, attention deficits, and changes in sleep-wake regulation. The frontal lobe is less like a discrete module and more like a switchboard that routes signals across the rest of the brain. Removing it does not leave a neat hole. It rewires, or fails to rewire, the entire system.