Corpus Callosum and W.J Case study

Corpus Callosum

Bundle of ~200 million myelinated axons; interconnects homologous regions of the two cerebral hemispheres; shorter rostrocaudally than the hemispheres; fibers to frontal and occipital poles curve forward and backward respectively.

Callosotomy

Surgical severing of the corpus callosum to reduce severe epileptic seizures by preventing interhemispheric spread of seizure activity.

Agenesis of the Corpus Callosum (ACC)

Congenital absence of the corpus callosum; can be complete, partial, or atypical; may occur alone or with other CNS/systemic malformations; more common in males; frequency in U.S. reported as 0.7%-5.3%.

Visual Information Transfer in Split-Brain Patients

Right visual field → left hemisphere (language dominant) → can verbally report objects. Left visual field → right hemisphere (non-language) → cannot verbally name object but can identify by left-hand touch.

Partial Callosal Lesions

Posterior regions transfer sensory info (vision, audition, somatosensory). Anterior regions transfer attentional and higher cognitive information.

Forebrain Commissures

Include corpus callosum, hippocampal commissure, anterior commissure, and massa intermedia; can compensate by assuming functions of the damaged hemisphere.

Callosal Lesions and Neighboring Structures

Often accompanied by damage to nearby brain regions; these neighborhood signs can overshadow pure callosal disconnection signs.

Callosal Agenesis and Disconnection Signs

Congenital ACC usually does not show classic disconnection symptoms, a puzzling phenomenon in clinical research.

Social Ordinariness of Split-Brain Patients

In everyday social interactions, patients appear normal; specialized testing (e.g., lateralized input tasks) is needed to reveal deficits.

Lack of Interhemispheric Transfer

Patients cannot retrieve with one hand an object felt with the other; mirrors findings in split-brain animal studies.

Left-Hand Tactile Anomia

Right-handed split-brain patients cannot name or describe objects placed in the left hand, even when they can manipulate them correctly.

Compensatory Phenomena in Split-Brain Patients

Patients develop strategies such as saying aloud the name of an object felt in the right hand so the right hemisphere can recognize the word and allow the left hand to identify it.

Left-Hand Verbal Dyspraxia

Due to disrupted callosal transfer: verbal commands are understood by the left hemisphere but cannot be carried out by the left hand, which relies on right hemisphere control.

Postcommissurotomy Mutism

Temporary inability to vocalize or produce speech sounds following commissurotomy.

Right Verbal Anosmia

Patients with callosal disconnection cannot name odors presented only to the right nostril.

W.J. Patient Background

48-year-old epilepsy patient who underwent callosotomy to prevent seizures from spreading between hemispheres.

W.J. Post-Surgery Finding - Two Minds

After callosotomy, W.J.'s hemispheres functioned independently, behaving as if he had two separate minds.

W.J. Left vs. Right Hand Performance

Right hand (left hemisphere): failed visuospatial tasks. Left hand (right hemisphere): succeeded in visuospatial tasks.

W.J. Visual Field and Language

Right visual field (left hemisphere): could name objects. Left visual field (right hemisphere): could not name objects but could identify them by pointing with left hand.

W.J. Significance for Hemispheric Specialization

Findings showed left hemisphere dominance for language and right hemisphere superiority in visuospatial processing.

W.J. Contribution to Brain Research

Case provided strong evidence for hemispheric specialization and localization of function in humans.