“Freezing of Gait: why and how?” – Lecture notes

A neurologist spoke on “freezing of gait” (FOG) at the early-April Insight 2020 conference. FOG occurs when an individual finds that his/her feet “stick” to the floor or shuffle forward in short, unbalanced steps, while they are trying to walk forward. FOG can make it difficult to get around and often precipitates falls. The lecture is a rather technical explanation of how FOG occurs. FOG is present in Parkinson’s Disease (PD) and all of the atypical parkinsonism disorders.

Insight 2020 was the largest online conference for people with PD, their caregivers, and those who work with the PD community. Lauren Stroshane from Stanford Parkinson’s Community Outreach attended the virtual conference and took notes on some of the talks that seemed most interesting. Copied below are her notes from a talk by neurologist Dr. Aasef Shaikh from the Cleveland Medical Center on the topic of FOG.


Freezing of gait: why and how?
Speaker: Dr. Aasef G. Shaikh, Assistant Professor of Neurology at Cleveland Medical Center
Insight into Parkinson’s Conference, April 2, 2020
Notes by Lauren Stroshane, Stanford Parkinson’s Community Outreach

Freezing of gait (FOG) occurs when an individual – most often, someone with Parkinson’s Disease (PD) – finds that their feet “stick” to the floor or shuffle forward in short, unbalanced steps, while they are trying to walk forward. Many with PD will experience some degree of FOG over the course of the illness; it can make it very difficult to get around, and often precipitates falls.

FOG is a context-dependent phenomenon: it doesn’t happen in every situation. Scenarios that commonly trigger FOG include:

  • Walking in a narrow hallway
  • Going in and out of a doorway or threshold where the flooring changes
  • Walking in a busy room with many people around, such as a grocery store

What is the common element in all these scenarios that leads to FOG in those with PD? It is not just a motor issue. Gait and balance in PD involve multiple systems. 

Action and perception are closely linked; if you perform a repetitive physical task and you perceive that you did it well, such as taking a step forward, then your brain interprets this as successful and repeats it. There seems to be a mismatch in PD between the perception of walking versus the action of walking. Postural changes and muscle rigidity often alter one’s center of gravity and ability to maintain normal balance; these also play into the likelihood of falls and freezing.

Visual and spatial processing difficulties are also common in PD and contribute to FOG and falls. If your brain is struggling to determine whether a dark shape at the end of the hall is a shadow, a table, or a dog, this can trigger freezing. Changes in depth perception, blurred vision, and double vision can occur in PD as well and are called binocular disparity. Tiny eye movements called saccades are normal for our regular visual processing; in PD, these saccades are often abnormal, making it more difficult for those with PD to scan their visual environment. Interestingly, those with Deep Brain Stimulation (DBS) implants seem to have improved eye movements compared with those who do not have DBS.

Putting all these factors together, as a person with PD is walking forward in their environment, impaired visuospatial processing and visual problems make it difficult to get a correct read on their surroundings, while motor issues and impaired ability to perceive their own movements make it difficult to know where in space their own body is. This mismatch seems to confuse the brain, leading to FOG as the brain struggles to figure out what to do.