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Regarding the recent postings relative to gait I felt compelled to get my 2-cents in..... There are, I would suggest, two distinct categories of freezing. One which generally occurs while in the "off" state and is visually mediated and another which occurs in the "on" state and is mediated by what I term the "T" factor (more later). There are also two categories of gait. One I call automatic gait and can be performed without conscious attention - it is the kind of walking one performs while strolling down an obstacle-free, level country lane. One can, for example easily carry on a conversation with a friend while performing automatic gait. The second category of gait is what I call "externally cued" gait - i.e. the environment cues the gait. Fording a stream by stepping on randomly protruding rocks is an example of externally cued gaiit. Automatically cued gait can also be called internally cued gait because each succeeding step is cued by the previous one, independent of the environment as long as the environment remains compatible with automatic gait. The most important parameter required for sustaining this self-cuing automatic gait is stride length. As long as the stride length exceeds a certain minimal threshhold, internally cued automatic gait is sustained. When the environment imposes a situation that requires a reduction in stride length below this minimal stride length threshhold we must shift from internally cued automatic gait to externally cued, conscious gait. In PD with associated gait pathology, the pathology is such that automatic gait can indeed be performed but is very difficult to access (i.e. initiate) and vulnerable to breaking down, but internally cued gait (where the environment dictiates varying stride length gaits below the minimal threshhold stridelength), cannot be accessed because in PD with associated gait pathology, we have only two stride lengths available, 1. the minimal threshhold stride length asssociated with automatic gait and 2. the very, very short stride length associated with festinaing gait (or in some cases no stride length at all). Turning or quick maneuvering is an environmentally dictated event which imposes the necessity to attenuate one's stride length. Thus, if one is walking along (automatic gait) and someone approaches there is a need to manuever which requires a shortened stridelength which in PD is not available which results in freezing. Sustaining automatic gait is dependent upon the reliable processing of dependable peripheral data. If such data is absent (e.g. walking down long corridors with nothing on the walls) or if such data cannot be seen (e.g. approaching a doorway framed by walls on either side which prevent one from seeing peripherally upstream) or if the data is misinterpreted (e.g. you are in your car, stopped at an intersection and the parked car visible peripherally begins to back up) freezing will occur. T-factor mediated freezing occurs as a consequence of a disturbance in the dynamic balance or interaction of excitatory and inhibitory neurotransmitters. It occurs in the presence or absence of therapeutic dopamine levels. It also results in an akinesia or freezing which is not vision mediated. I'll save this for a future discussion. Regards. tom