freezing of gait ( fog ) is characterized by start and turn hesitation and is a common clinical feature in parkinson 's disease ( pd ) . the sudden appearance of fog can increase the risk of falls and reduce the quality of life . there are several therapeutic approaches , such as medications ( l - dopa or deprenyl )   and external stimuli ( visual or auditory cues ) , to reduce fog , but their effects are usually limited for most pd patients . recently , pd patients with severe fog were reported to be able to ride a bicycle [ 3 , 4 , 5 ] . we studied whether imagining bicycling alone provided improvement in severe fog without a good response to external stimuli , such as visual and auditory cues , or whether imagining and mimicking bicycling after having initiated gait was effective for alleviating the interruption of gait in 2 pd patients . a 70-year - old woman noticed short shuffling steps and difficulty in turning her body while walking at the age of 67 . neurological findings at the age of 67 revealed a depressive state , masked face , resting tremor , cogwheel type rigidity , bradykinesia , severe fog , postural instability , and autonomic dysfunction , such as pollakisuria , constipation , and orthostatic hypotension . after gradual increases of l - dopa / decarboxylase inhibitor ( dci ; 200900 mg / day ) and l - threo-3,4-dihydroxyphenylserine ( 100600 mg / day ) , these parkinsonian symptoms improved , except for the severe fog and postural instability ( fig . visual and auditory cues also did not improve severe fog and , therefore , her quality of life was limited . when she was instructed to imagine that she was pedaling a bicycle prior to trying to initiate gait imagining taking a large step , climbing stairs , or stepping over regular horizontal lines did not improve severe fog . when the patient was additionally instructed to imagine and mimic bicycling after having initiated walking , her gait was more rhythmical and without interruption ( online suppl . after several visits , severe fog in its normal condition without imagining bicycling and the improvement of fog after imagining bicycling were similar to the results shown in online supplementary video segments 1 and 2 . tc - ecd spect showed mild hypoperfusion in the anterosuperior frontal and posterolateral parietal lobes . the heart - to - mediastinum ( h / m ) ratio in i - metaiodobenzylguanidine myocardial scintigraphy decreased ( early h / m : 1.89 , delayed h / m : 1.68 ) . a 74-year - old woman found it difficult to begin walking at the age of 64 . neurological findings at the age of 66 revealed parkinsonism , such as microphonia , cogwheel type rigidity , bradykinesia , and fog . although the administration of l - dopa / dci ( 600 mg / day ) and ropinirole ( 12 mg / day ) , and visual and auditory cues did not improve the severe fog , she was able to walk without fog after imagining bicycling ( fig . video segment 4 ) , and the gait interruptions improved when imagining and mimicking bicycling after gait initiation ( online suppl . imagining taking a large step , climbing stairs , or stepping over regular horizontal lines did not improve severe fog . severe fog in its normal condition without imagining bicycling and the improvement of the fog after imagining bicycling were similar to the gaits shown in online supplementary video segments 3 and 4 after several visits . a 70-year - old woman noticed short shuffling steps and difficulty in turning her body while walking at the age of 67 . neurological findings at the age of 67 revealed a depressive state , masked face , resting tremor , cogwheel type rigidity , bradykinesia , severe fog , postural instability , and autonomic dysfunction , such as pollakisuria , constipation , and orthostatic hypotension . after gradual increases of l - dopa / decarboxylase inhibitor ( dci ; 200900 mg / day ) and l - threo-3,4-dihydroxyphenylserine ( 100600 mg / day ) , these parkinsonian symptoms improved , except for the severe fog and postural instability ( fig . visual and auditory cues also did not improve severe fog and , therefore , her quality of life was limited . when she was instructed to imagine that she was pedaling a bicycle prior to trying to initiate gait imagining taking a large step , climbing stairs , or stepping over regular horizontal lines did not improve severe fog . when the patient was additionally instructed to imagine and mimic bicycling after having initiated walking , her gait was more rhythmical and without interruption ( online suppl . after several visits , severe fog in its normal condition without imagining bicycling and the improvement of fog after imagining bicycling were similar to the results shown in online supplementary video segments 1 and 2 . tc - ecd spect showed mild hypoperfusion in the anterosuperior frontal and posterolateral parietal lobes . the heart - to - mediastinum ( h / m ) ratio in i - metaiodobenzylguanidine myocardial scintigraphy decreased ( early h / m : 1.89 , delayed h / m : 1.68 ) . a 74-year - old woman found it difficult to begin walking at the age of 64 . neurological findings at the age of 66 revealed parkinsonism , such as microphonia , cogwheel type rigidity , bradykinesia , and fog . although the administration of l - dopa / dci ( 600 mg / day ) and ropinirole ( 12 mg / day ) , and visual and auditory cues did not improve the severe fog , she was able to walk without fog after imagining bicycling ( fig . video segment 4 ) , and the gait interruptions improved when imagining and mimicking bicycling after gait initiation ( online suppl . imagining taking a large step , climbing stairs , or stepping over regular horizontal lines did not improve severe fog . severe fog in its normal condition without imagining bicycling and the improvement of the fog after imagining bicycling were similar to the gaits shown in online supplementary video segments 3 and 4 after several visits . fog in these pd patients showed a remarkably good response to imagining bicycling , but not to anti - parkinsonian drugs , or visual or auditory cues . this possibly indicates that the pathophysiological mechanisms of fog may include bilateral dyscoordination of steps [ 6 , 7 , 8 ] . although the mechanism by which imagining bicycling improved the fog remains unclear , the rhythmical movement of the legs ( i.e. alternating from side to side with one leg going up as the contralateral leg goes down ) may be engendered by imagining bicycling . attention does not seem to be highly related to the improvement of fog because imagining taking a large step , climbing stairs , or stepping over regular horizontal lines did not improve it . interestingly , their gait was rhythmical without interruption when imagining and mimicking bicycling after having initiated gait . imagining and mimicking bicycling during gait may be able to influence gait control through higher cortical function . visual cues require conspicuous horizontal lines on the floor , while auditory cues require an audio instrument , such as a metronome . these external stimuli are hard to be used out of the house . on the other hand , although further investigation with a larger number of samples is needed , imagining bicycling , or imagining and mimicking bicycling could serve as a novel and simple therapeutic approach for intractable fog or gait interruptions in pd patients .
freezing of gait ( fog ) is one of the factors that reduce the quality of life in patients with parkinson 's disease ( pd ) . imagining bicycling before gait start provided improvement in fog in 2 pd patients . imagining and mimicking bicycling after the initiation of gait allowed the rhythmic gait to continue without interruption . 
 we suggest that imagining and mimicking bicycling , which are nonexternal cues , could serve as a helpful therapeutic approach for the intractable freezing and interruption of gait of pd patients .