Hypergraphia is a behavioral condition characterized by the intense desire to write or draw. Forms of hypergraphia can vary in writing style and content. It is a symptom associated with temporal lobe changes in epilepsy and in Geschwind syndrome. Structures that may have an effect on hypergraphia when damaged due to temporal lobe epilepsy are the hippocampus and Wernicke's area. Aside from temporal lobe epilepsy, chemical causes may be responsible for inducing hypergraphia.

American neurologists Stephen Waxman and Norman Geschwind were the first to describe hypergraphia, in the 1970s. The patients they observed displayed highly compulsive detailed writing, sometimes with literary creativity. The patients kept diaries, which some used to meticulously document minute details of their everyday activities, write poetry, or create lists. Case 1 of their study wrote lists of her relatives, her likes and dislikes, and the furniture in her apartment. Beside lists, the patient wrote poetry, often with a moral or philosophical undertone. She described an incident in which she wrote the lyrics of a song she learned when she was 17 several hundred times and another incident in which she felt the urge to write a word over and over again. Another patient wrote aphorisms and certain sentences in repetition.

A patient from a separate study experienced continuous "rhyming in his head" for five years after a seizure and said that he "felt the need to write them down." The patient did not talk in rhyme, nor did he read poetry. Language capacity and mental status were normal for this patient, except for recorded right-temporal spikes on electroencephalograms. This patient had right-hemisphere epilepsy. Functional MRI scans of other studies suggest that rhyming behavior is produced in the left hemisphere, but Mendez proposed that postictal hypoactivity of the right hemisphere may induce a release of writing and rhyming abilities in the left hemisphere.

In addition to writing in different forms (poetry, books, repetition of one word), hypergraphia patients differ in the complexity of their writings. While some writers (e.g. Alice Flaherty and Dyane Harwood) use their hypergraphia to help them write extensive papers and books, most patients do not write things of substance. Flaherty describes hypergraphia as a result of decreased temporal lobe function which disinhibits frontal lobe idea and language generation, "sometimes at the expense of quality." Patients hospitalized with temporal lobe epilepsy and other disorders causing hypergraphia have written memos and lists (like their favorite songs) and recorded their dreams in extreme length and detail.

There are many accounts of patients writing in nonsensical patterns including writing in a center-seeking spiral starting around the edges of a piece of paper. In one case study, a patient even wrote backward, so that the writing could only be interpreted with the aid of a mirror. Sometimes the writing can consist of scribbles and frantic, random thoughts that are quickly jotted down on paper very frequently. Grammar can be present, but the meaning of these thoughts is generally hard to grasp and the sentences are loose. In some cases, patients write extremely detailed accounts of events that are occurring or descriptions of where they are.

In some cases, hypergraphia can manifest with compulsive drawing. The composer Robert Schumann, during periods of high musical output, also wrote many long letters to his wife Clara; similarly, Vincent van Gogh had much more written correspondence during bouts of intense painting. Many drawings by patients with hypergraphia exhibit repetition and a high level of detail, sometimes mixing both compulsive writing and drawing together.

Some studies have suggested that hypergraphia is related to bipolar disorder, hypomania, and schizophrenia. Although creative ability was observed in the patients of these studies, signs of creativity were observed, not hypergraphia specifically. Therefore, it is difficult to say with absolute certainty that hypergraphia is a symptom of these psychiatric illnesses because creativity in patients with bipolar disorder, hypomania, or schizophrenia may manifest into something aside from writing. However, other studies have shown significant accounts between hypergraphia and temporal lobe epilepsy and chemical causes.

Hypergraphia was first studied as a symptom of temporal lobe epilepsy, a condition of reoccurring seizures caused by excessive neuronal activity, but it is not a common symptom among patients. Less than 10 percent of patients with temporal lobe epilepsy exhibit characteristics of hypergraphia.^{[medical citation needed]} Temporal lobe epilepsy patients may exhibit irritability, discomfort, or an increasing feeling of dread if their writing activity is disrupted. To elicit such responses when interrupting their writing suggests that hypergraphia is a compulsive condition, resulting in an obsessive motivation to write. A temporal lobe epilepsy may influence frontotemporal connections in such a way that the drive to write is increased in the frontal lobe, beginning with the prefrontal and premotor cortex planning out what to write, and then leading to the motor cortex (located next to the central fissure) executing the physical movement of writing.