Cognitive performance and brain dynamics during walking with a novel bionic foot: A pilot study

Abstract

Objectives: The objectives are to determine neural dynamics during gait using electro-encephalography and source localization, and to investigate the attentional demand during walking in able-bodied individuals, and individuals with an amputation.

Materials & methods: Six able-bodied individuals conducted one experimental trial, and 6 unilateral transtibial and 6 unilateral transfemoral amputees performed 2 experimental trials; the first with the prosthesis currently used by the subjects and the second with a novel powered transtibial prosthesis, i.e. the Ankle Mimicking Prosthetic foot 4.0. Each experimental trial comprised 2 walking tasks; 6 and 2 minutes treadmill walking at normal speed interspersed by 5 minutes of rest. During 6 minutes walking the Sustained Attention to Response (go-no go) Task, which measures reaction time and accuracy, was performed. Electro-encephalographic data were gathered when subjects walked 2 minutes. Motor-related cortical potentials and brain source activity during gait were examined. Normality and (non-) parametric tests were conducted (p<0.05).

Results and discussion: In contrast to transtibial amputees, transfemoral amputees required more attentional demands during walking with Ankle Mimicking Prosthetic foot 4.0 compared to the current passive prosthetic device and able-bodied individuals (reaction time and accuracy: p≤0.028). Since risk of falling is associated with altered attentional demands, propulsive forces of the novel device need to be better controlled for transfemoral amputees. No motor-related cortical potentials at Cz were observed in transfemoral amputees walking with the novel prosthesis, whereas motor-related cortical potentials between transtibial amputees and able-bodied individuals during walking at normal speed did not differ. The first positive electro-physiological peak deflection appeared during toe-off phase and showed higher activity within the underlying brain sources in transtibial amputees walking with Ankle Mimicking Prosthetic foot 4.0 compared to able-bodied individuals. The required higher neural input to accomplish the same physical activity compared to able-bodied individuals is possibly due to the limited acclimation period to the novel device and consequently increased afferent sensory feedback for postural control.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Presents the Consort flow diagram (enrolment, allocation and analysis).

After the familiarization trial, two experimental trials were conducted; the first trial was performed with the current prosthesis and the second trial with the AMPfoot (4.0) (Fig 2). The AMPfoot 4.0 was fitted by a professional prosthetist using individualized connectors and shanks. Furthermore, subjects were familiarized with the novel device for about 15 to 30 minutes preceding experimental trial 2. The AMPfoot 4.0 design is also based on previous research conducted on the AMPfoot 2 [15] and 3 [16]. However, it is important to note that in contrast with its preceding designs, the AMPfoot 4.0 does not provide active propulsion at push-off.

Fig 2. Experimental design and protocol.

Dual-task walking was performed during the 6 minutes walk test. The cognitive task consisted of ten digits [0 1 2 3 4 5 6 7 8 9] randomly displayed for 250ms on a screen positioned in front of the subject followed by a 900ms mask. After a 5 minutes rest period subjects conducted the 2 minutes walk test and EEG was reapplied on the subjects’ head.

Fig 3. Shows reaction times (ms) of all subject groups at baseline and during dual-task walking.

Fig 4. Accuracy of the no go stimuli during the middle part (Accuracy3) and at the end of the cognitive task (Accuracy5) for TFA walking with AMPfoot compared to TFA walking with the current prosthesis, TTA walking with the AMPfoot and able-bodied walking.

Fig 5. Shows a smoothed scatterplot showing EEG waveform (two positive deflections P1 and P2, and two negative deflections N1 and N2) recorded over the Cz electrode during an averaged gait cycle of able-bodied individuals and TTA with current and novel prosthetic devices.

Standard deviations are visualized for both x and y axes. An example of gait cycle phases and events is shown below the graph (here: force-sensing resistor placed in right insole). RHS: right heel strike, RTO: right toe off, LHS: left heel strike, LTO: left toe off.

Fig 6. Displays a smoothed scatterplot showing individual EEG waveforms (at C3 or F3) during a gait cycle of TFA walking with current prosthetic device.

The black line represents the average of the 5 TFA. S2 is the only TFA with left amputation and therefore the dashed line represents the average of 4 TFA with right amputation. An example of gait cycle phases and events is shown below the graph (here: force-sensing resistor placed in left insole). RHS: right heel strike, RTO: right toe off, LHS: left heel strike, LTO: left toe off.

Fig 7

Orthogonal views of higher activity (coloured in yellow and red) of brain sources of MRCP P1 when TTA walked with AMPfoot compared to able-bodied individuals (L: left, R: right, A: anterior, P: posterior, I: inferior, S: superior). Force-sensing resistors were placed under the right foot, explaining the higher activity at P1 (phase between weight acceptance and single-limb support during gait) at the left hemisphere of the brain.