Final answer:
Lesions in the primary somatosensory cortex, specifically the postcentral gyrus of the parietal lobe, can lead to an increased somatosensory threshold in the contralateral body side.
Step-by-step explanation:
Lesions in the postcentral gyrus of the parietal lobe, which is identified as Brodmann's areas 1, 2, and 3 and known as the primary somatosensory cortex, can cause an increase in the somatosensory threshold in the contralateral side of the body. This part of the brain processes various tactile sensations including touch, pressure, pain, and proprioception. Damage to this area may result in decreased perception of these sensations on the side of the body opposite to the lesion. This is because the sensory pathways for somatosensation cross over to the opposite side of the brain at the level of the spinal cord or lower brainstem before reaching the somatosensory cortex.