Neurons in Area 5 of the Posterior Parietal Cortex in the Cat Contribute to Interlimb Coordination During Visually Guided Locomotion: A Role in Working Memory

Abstract

We tested the hypothesis that area 5 of the posterior parietal cortex (PPC) contributes to interlimb coordination in locomotor tasks requiring visual guidance by recording neuronal activity in this area in three cats in two locomotor paradigms. In the first paradigm, cats were required to step over obstacles attached to a moving treadmill belt. We recorded 47 neurons that discharged in relationship to the hindlimbs. Of these, 31/47 discharged between the passage of the fore- and hindlimbs (FL-HL cells) over the obstacle. The activity of most of these neurons (25/31) was related to the fore- and hindlimb contralateral to the recording site when the contralateral forelimb was the first to pass over the obstacle. In many cells, discharge activity was limb-independent in that it was better related to the ipsilateral limbs when they were the first to step over the obstacle. The other 16/47 neurons discharged only when the hindlimbs stepped over the obstacle with the majority of these (12/16) discharging between the passage of the two hindlimbs over the obstacle. We tested 15/47 cells, including 11/47 FL-HL cells, in a second paradigm in which cats stepped over an obstacle on a walkway. Discharge activity in all of these cells was significantly modulated when the cat stepped over the obstacle and remained modified for periods of ≤ 1 min when forward progress of the cat was delayed with either the fore- and hindlimbs, or the two hindlimbs, straddling the obstacle. We suggest that neurons in area 5 of the PPC contribute to interlimb coordination during locomotion by estimating the spatial and temporal attributes of the obstacle with respect to the body. We further suggest that the discharge observed both during the steps over the obstacle and in the delayed locomotor paradigm is a neuronal correlate of working memory.

Stability of gait and interlimb coordination in older adults

“…Furthermore, the finding that the response observed in both young and older adults involved the whole body may indicate the involvement of a central mechanism. It is well known that in cats, the motor cortex and specifically the corticospinal tract are involved in obstacle avoidance during gait by modifying forelimb elevation according to obstacle characteristics (Drew 1988(Drew , 1993Lajoie et al 2010). Microstimulation of pyramidal tract neurons generated a phase shift in the locomotor patterns in the cat hindlimb (Orlovsky 1972) similar to phase shifts observed in this study.…”

Electrocortical activity is coupled to gait cycle phase during treadmill walking

“…Prior research using functional magnetic resonance imaging has implicated the posterior parietal cortex in upper-limb reaching (Filimon et al, 2009) and in coordination of left and right wrist movements . In addition, microwire arrays implanted into feline posterior partial and motor cortex during flat ground and precision walking have suggested that visuo-motor integration during locomotion is critically dependent on posterior parietal and motor cortex networks Beloozerova and Sirota, 2003;Drew et al, 2002;Lajoie et al, 2010). In our study, we found (with one exception) that within a given frequency band (alpha, beta, or high-gamma) spectral power fluctuations were synchronous across all four electrocortical domains but were not uniformly significant (i.e.…”

“…In feline posterior parietal cortex Beloozerova and Sirota, 2003;Lajoie et al, 2010) and motor cortex (Armstrong and MarpleHorvat, 1996;Drew, 1993;Drew et al, 2002;Widajewicz et al, 1994) neuronal firing rates exhibit peaks that are synchronized to the gait cycle. These studies suggest that feline posterior parietal cortex likely plays a role in visuo-motor integration during locomotion while motor cortex contributes to gait execution.…”

EphA4-Mediated Ipsilateral Corticospinal Tract Misprojections Are Necessary for Bilateral Voluntary Movements But Not Bilateral Stereotypic Locomotion

“…In spinal cord, ephrinB3 is a midline axon repellant protein (Kullander et al, 2001b). Elimination of ephrinB3, EphA4, or the adapter protein ␣2-Chimaerin results in aberrant bilaterally projecting spinal interneurons (Kullander et al, 2001a;Yokoyama et al, 2001;Kullander et al, 2003;Beg et al, 2007;Iwasato et al, 2007;Wegmeyer et al, 2007;Asante et al, 2010), many of which are central pattern generator (CPG) components . Instead of an alternating gait during overground and treadmill locomotion, null mutants have a hopping gait (Akay et al, 2006).…”