Brain activity associated with pain, hyperalgesia and allodynia: an ALE meta-analysis

The use of functional brain imaging techniques offers the possibility of uncovering the cerebral processing of the human pain experience. In recent years, many imaging studies have focused on defining a network of brain structures involved in the processing of normal pain. Additionally, it has been shown that stimulus-evoked pain, which is a frequent symptom of neuropathic pain, causes distinct patterns of brain activation. In the present study, we quantitatively analyzed the data of previous functional imaging studies. Studies were thus collected by means of a MEDLINE query. A meta-analysis using the activation-likelihood estimation method was conducted to quantify the acquired results. We then used this data to summarize and compare the cerebral activations of (i) normal and stimulus-evoked pain, (ii) thermal and mechanical pain, (iii) different types of stimulus-evoked pain (hyperalgesia, allodynia), and (iv) clinical neuropathic and experimental pain. The results suggest the existence of distinct, although overlapping, neuronal networks related to these different types of pain.