Active-state functional connectivity

Task-positive and task-negative brain networks (Fox et al, 2005)

I’m currently preparing for a talk on a recent paper (Powers et al, 2011) using resting-state functional connectivity MRI to study large-scale networks in the human brain. (Okay, actually I’m procrastinating working on the talk by writing this post.) Different brain regions are anatomically connected via projections from one area to the next, allowing long-range communication across the brain. This functional connectivity can be observed as synchronized BOLD signal in connected regions while a person is at rest or performing a task, and such correlated areas have been found to correspond with functional sub-networks within the brain. For instance, an extensive “task-positive” network (shown in warm colors at right, from Fox et al, 2005) is thought to comprise multiple sub-networks including, for example, a task control system composed of the dorsal anterior cingulate and frontal operculum, and a dorsal attention system involving areas of superior frontal and parietal cortex.

While out for a run yesterday I was struck by the remarkable parallel between such integrated brain systems and our non-brain “networks” of muscle, fascia, tendons and ligaments that coordinate distinct yet complementary functions while we run. Unfortunately but necessarily, this appreciation was triggered by the heightened bodily awareness that accompanies injury. About a month ago during a particularly intense and hilly run, I noticed a nagging tension in both hip flexors. I followed this the next day with a short, easy barefoot run during which a dull ache appeared on the top of my foot. Simply a classic case of the novice barefooter’s too-much-too-soon, right? Over the subsequent weeks, I’ve dealt with recurring minor flare-ups of both these top-of-foot and hip issues and assumed they were unrelated and exacerbated by distinct factors – my continued increase in barefoot / minimalist mileage and hill running, respectively.

But it wasn’t until my monthly sports massage this week that I learned just how connected – possibly causally related – these problems were. As my therapist applied pressure just lateral to my hip flexor a subtle burning appeared in my extensor tendon along the shin and foot. Release of hip pressure … relief of extensor ache. Application of hip pressure … return of extensor pain. And so on. I was astounded by the consistency of this pattern to the point that I even questioned my own sensations. There was an undeniable connection between my hip flexor and extensor, such that tension in one translated into pain and impaired function in the other. Although I’m not happy to report that my “anterior leg network” hasn’t fully recovered, its continued dysfunction has further highlighted the strong connectivity I suspected during the massage. While running a moderate uphill climb yesterday, my hip flexor predictably tightened up. Moments later, an ache appeared along the top of my foot and ankle. Then – just to mix things up, my knee began to burn as I felt my knee cap riding out of alignment. While certainly not a pleasant finale to the run, this sudden cascade of pains clearly demonstrated a deeply integrated anterior chain, from foot to knee to hip – and likely beyond.

Tom Meyers' Anatomy Trains

A clear picture of functional brain organization requires understanding not only the role of single units – a neuron or isolated region, but also the critical interactions between such elements. Similarly, effective communication within and across our musculoskeletal sub-systems, along with an integration of mind with body, is essential to properly function as a runner. The springy tendons of the foot cannot propel us along without power from our quads and gluts, stability from our core, and motor commands from and sensory feedback to the brain, together coordinating a smooth, fluid ride.

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