Prefrontal Cortex Activation During Dual Task With Increasing Cognitive Load in Subacute Stroke Patients: A Pilot Study

Abstract

Stroke patients often exhibit difficulties performing a cognitive task while walking, defined as a dual task (DT). Their prefrontal cortex (PFC) activity is higher in DT than in single task (ST). The effects of an increasing load on PFC activity during DT in subacute stroke patients remains unexplored. Our objective was to assess the effects of N-back tasks (low/high load) on cerebral activity, gait parameters, and cognitive performances. Eleven subacute stroke patients (days post-stroke 45.8 ± 31.6) participated in this pilot study (71.4 ± 10 years, BMI 26.7 ± 4.8 kg.m −2 , Barthel index 81.8 ± 11.0). Patients completed a ST walk , and 4 conditions with 1-back (low load) and 2-back (high load): ST low , ST high , DT low , and DT high . Overground walking was performed at a comfortable pace and -N-back conditions were carried out verbally. Both gait (speed, stride variability) and cognitive (rate of correct answers) performances were recorded. Changes in PFC oxyhemoglobin (ΔO 2 Hb) and deoxyhemoglobin (ΔHHb) were measured by functional near infrared spectroscopy (fNIRS). Results showed an increase of ΔO 2 Hb while walking, which was not augmented by cognitive loads in DT. Walking speed was reduced by low and high cognitive loads in DT compared to ST walk ( P < 0.05), but was not different between DT low and DT high . Cognitive performances were negatively impacted by both walking ( P < 0.05) and cognitive load (between “low” and “high,” P < 0.001). These data highlight a “ceiling” effect in ΔO 2 Hb levels while walking, leaving no available resources for simultaneous cognitive tasks, during the early recovery period following stroke. In these patients, cognitive, but not motor, performances declined with a higher cognitive load.

Functional Status Is Associated With Prefrontal Cortex Activation in Gait in Subacute Stroke Patients: A Functional Near-Infrared Spectroscopy Study

“…LoB patients required additional attentional resources for walking, in accordance with our previous work in which ST mot and cognitive-motor DT induced a PFC overactivation (vs. ST cog ) in subacute stroke patients (8). We had highlighted the existence of a "ceiling" phenomenon in brain oxygenation induced by walking: a brain overactivation in stroke patients could be triggered by ST mot and could not be further augmented by an additional cognitive load in DT (8). The present study evidences a similar phenomenon only for LoB patients, which illustrates a greater reliance on cortical control of gait in patients with poor mobility.…”

“…In conclusion, our study highlights a PFC overactivation in the unaffected side for less functional stroke patients, triggered in walking conditions (ST mot ), potentially limited by an upper limit that may not be exceeded in DT (8). This would likely be due to the loss of stepping automaticity in ST (i.e., higher-level control of gait) and then is not observed in more autonomous stroke patients.…”

“…Studies using fNIRS reported a greater brain activity in the PFC during DT than in single task (ST) in chronic stroke patients, implying that executive functions were primary involved in this overactivation ( 6 , 7 ). Recently, we observed no difference of oxygenated hemoglobin levels (ΔO 2 Hb) between motor ST and DT in subacute stroke patients ( 8 ), highlighting a ceiling effect on brain activity observed in DT and thus the loss of stepping automaticity in these patients.…”

“…Responses were recorded with a voice recorder. The percentage of correct answers was computed for each cognitive condition, as missing or incorrect answers were accounted for as errors (8). In walking ST mot and DT, patients walked through an open space at a comfortable pace for 30 s, through an 8-m GAITRite walkway (Sparta, USA), which provided speed and stride variability.…”

Cerebral Oxygenation Reserve: The Relationship Between Physical Activity Level and the Cognitive Load During a Stroop Task in Healthy Young Males

“…Oxysoft version 3.0 software (Artinis Medical Systems, Elst, Netherlands) was used for data collection. This protocol for optode positioning has been used successfully in recent studies [44,45].…”