A 52-year-old man from Delhi presents with a 3-month history of progressive weakness in both lower limbs with spasticity. On examination, he has hyperreflexia and bilateral Babinski sign. Vibration and proprioception are intact, but he has loss of pain and temperature sensation below the level of T6 dermatome bilaterally. Gait is stiff and scissor-like. MRI spine shows a central cord lesion at T5–T6 with syrinx formation. Which spinal tract is most likely damaged to explain the dissociated sensory loss?