Six years ago we blogged about the 5th edition of the classic textbook on The Neurology of Eye Movements by Leigh & Zee, which had just been published, using a three part series to share some of its highlights (Part1, Part 2 and Part 3).
This book is a gem, and I was toying with the idea of doing a selective chapter review much as we did for Kandel’s Principles of Neural Science which took eleven parts (as a refresher, here is Part 1 and here is Part 11). I’m not sure that’s what we’ll do, but let’s begin with some highlights from Chapter 1 which opens in noting that abnormalities of ocular motility frequently provide diagnostic clues to clinicians – including neurologists, ophthalmologists, optometrists, and otolaryngologists, and that eye movements have been used to gain insights into disorders ranging from muscular dystrophy to autism.
Leigh and Zee write: “At the level of cognition, eye movements have provided insights into faculties such as memory, decision making, task-switching, and reward, as well as psychotic thought disorders. Indeed, as functional imaging has demonstrated, activity related to eye movements can be found in almost every corner of the brain.”
Here is a sampling of insights from Chapter 1 that sets the stage for what is to follow in subsequent chapters:
- Each of the EOMs have an inner layer that inserts on the globe and an outer layer that inserts onto fibromuscular pulleys that guide the muscle’s tendon. The relationship between neural commands and eye rotations remains linear, likely because the tissues of the orbit act as an analog computer to simplify the brain’s computations.
- The dynamic properties of the vestibulo-ocular reflex (VOR) undergo adaptive changes in order to maintain optimal visuo-motor performance.
- The translational VOR (t-VOR) minimizes relative motion between images of the near target with respect to the distant stationary background. (Hence when you do do motion parallax with vectograms, you are directly tweaking neurology of the t-VOR).
- Compared to the VOR, the control of smooth pursuit is less precise due to inherent noisy transformation that occur in cortical areas concerned with motion. The brain uses a Bayesian strategy, associated with prediction and learning, to deal with imprecise processing of visual cues.
- The functional division in the way the visual system processes objects in the environment involves a ventral stream of projections concerned with perceptual identification and a dorsal stream concerned with the sensorimotor transformations required to guide motor responses to such objects.