Critical Relay in Visual Circuit of the Brain May Help Explain LD

Science Magazine, July 25, 2003, reports on a new study from Harvard Medical School. The study looks at a key brain structure, called the subplate, that is part of the relay of information from the receptors of the eye’s retina to the brain. This study, done on cats, may provide insight into early brain defects associated with learning disabilities.

Hubel and Wiesel, of the Harvard Medical School, studying the visual processing of cats, demonstrated a clear pattern of organization in the cortex following visual experience. Neural connections starting in a region that receives input from the thalamus, the lateral geniculate nucleus (LGN), a region of the thalamus that receives input from the cells on the retina at the back of the eye, are processed to the cortex where they are organized in highly specialized columns. Hubel and Wiesel won the Nobel Prize for their significant discoveries.

The current research looked at the subplate, a rarely studied structure that is a connection between the thalamus and the cortex. This region is highly susceptible to damage. Without an effective subplate the organization of columns within the cortex, and thus visual information suffers. The researchers found that neural activity and signals between the LGN and the cortex were much weaker in the brains of cats missing the subplate brain cells (neurons).