**1. Introduction**

Pain still remains a challenge for clinicians and neuroscientists, and current pharmacological therapies are often ineffective for the prevention and treatment of chronic pain. In particular, chronization of pain represents a multi-step phenomenon, comprising spinal phenotypic switch in the expression of neuropeptides, as well as elusive brain mechanisms, ranging from the so-called "thalamo-cortical dysrhythmia" to a functional reorganization of sensorimotor maps (**Figure 1**) [1–4]. In this scenario, the putative relationship between pain and the cerebellum is particularly intriguing, as the cerebellum is anatomically located between the spinal cord and the brain, possibly interfering both with top-down and bottom-up mechanisms underlying pain control and ultimately responsible for central pain sensitization.

The cerebellum is involved in a wide range of integrative functions, ranging from motor adaptation to working memory and associative learning, but its role in nociceptive experience and pain processing remains debated [5–10].

Overall, the cerebellum likely belongs to a widespread network that mediates reactions stronger to negative external stimuli than to positive ones [11, 12]; recent

### *Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

#### **Figure 1.**

*"Red Flags" responsible for chronization of pain. Chronic pain is a multi-level and multi-step phenomenon, comprising changes at brain as well as spinal levels, and involves different neurotransmitters and neuronal pathways.*

### **Figure 2.**

*Rationale for the use of cerebellar tDCS (tcDCS) for pain treatment: possible mechanisms of action and molecular pathways.*

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firing rate.

*Cerebellar Transcranial Direct Current Stimulation (ctDCS) Effect in Perception…*

engagement both in pain empathy and nocifensive withdrawal [18–20].

emerging field of non-invasive neuromodulation (**Figure 2**).

**2. Current pitfalls for the use of NIBS in pain treatment**

"placebo-effect." There are also other possible explanations.

evidence has strengthened the hypothesis that plasticity subserving the storage and retention of unconditioned responses selectively occurs in the cerebellum [13–16]; recently we have proved a cerebellar role in learning of aversive reactions inside the peripersonal space [17], and studies in humans have highlighted a cerebellar

Nonetheless, some important questions remain open: (1) whether the cerebellum is engaged in the primary sensory-discriminative dimension of pain; (2) how it interacts with the cerebral cortex for pain processing; (3) whether it may be used as a putative target for non-pharmacological therapies, as non-invasive brain stimula-

In this chapter, we encompass the current knowledge about the cerebellar role in pain processing, suggesting novel strategies for pain control and therapy in the

Cerebellar direct current stimulation has been widely used for the treatment of several neuropsychiatric diseases, ranging from movement disorders [21–25] to autism and schizophrenia [26, 27], but only few evidence has been reached so far

In general, transcranial direct current stimulation (tDCS) has been proposed for pain therapy, especially when applied over the primary motor area (M1) or the dorsolateral prefrontal cortex [28, 29]; nonetheless, the too small sample sizes and the extreme variability of stimulation parameters have limited its efficacy: as a result, pain improvement is often weak and brief, in line with the so-called

First, pain is a complex experience, involving phenomena at a sensory, affective-

Third, only few groups have enough experience about the use of neurophysiological tools for pain assessment [30]; among these techniques, laser evoked potentials (LEPs) offer an unique opportunity to study the sensory-discriminative, as well as the affective-emotional dimension of pain, which are differently carried by medial and lateral spinal nociceptive systems and rely on the activation of distinct

**3. Transcranial direct current stimulation (tDCS) and the cerebellum:** 

**3.1 Putative mechanisms of action of cerebellar tDCS and implications for pain** 

Transcranial direct current stimulation (tDCS) has emerged in the past few years as a novel, noninvasive, inexpensive, and safe technique to modulate cortical excitability, both in health and disease. tDCS uses subthreshold currents (1.0–2.5 mA), too weak to induce neuronal activity independent from afferent input, but sufficient *per se* to alter both the excitability and spontaneous neuronal

emotional and cognitive level: thus, clinical scales are often inappropriate to describe the whole phenomenon and follow putative effects of therapies over time. Second, chronic pain involves different neurotransmitters and neuronal circuitries at a spinal and supra-spinal level: therefore, non-invasive stimulation applied

over a limited brain target usually induces a transient pain improvement.

*DOI: http://dx.doi.org/10.5772/intechopen.89805*

tion techniques (NIBS).

regarding pain therapy.

cortical areas [31–33].

**an overview**

**treatment**

*Cerebellar Transcranial Direct Current Stimulation (ctDCS) Effect in Perception… DOI: http://dx.doi.org/10.5772/intechopen.89805*

evidence has strengthened the hypothesis that plasticity subserving the storage and retention of unconditioned responses selectively occurs in the cerebellum [13–16]; recently we have proved a cerebellar role in learning of aversive reactions inside the peripersonal space [17], and studies in humans have highlighted a cerebellar engagement both in pain empathy and nocifensive withdrawal [18–20].

Nonetheless, some important questions remain open: (1) whether the cerebellum is engaged in the primary sensory-discriminative dimension of pain; (2) how it interacts with the cerebral cortex for pain processing; (3) whether it may be used as a putative target for non-pharmacological therapies, as non-invasive brain stimulation techniques (NIBS).

In this chapter, we encompass the current knowledge about the cerebellar role in pain processing, suggesting novel strategies for pain control and therapy in the emerging field of non-invasive neuromodulation (**Figure 2**).

### **2. Current pitfalls for the use of NIBS in pain treatment**

Cerebellar direct current stimulation has been widely used for the treatment of several neuropsychiatric diseases, ranging from movement disorders [21–25] to autism and schizophrenia [26, 27], but only few evidence has been reached so far regarding pain therapy.

In general, transcranial direct current stimulation (tDCS) has been proposed for pain therapy, especially when applied over the primary motor area (M1) or the dorsolateral prefrontal cortex [28, 29]; nonetheless, the too small sample sizes and the extreme variability of stimulation parameters have limited its efficacy: as a result, pain improvement is often weak and brief, in line with the so-called "placebo-effect." There are also other possible explanations.

First, pain is a complex experience, involving phenomena at a sensory, affectiveemotional and cognitive level: thus, clinical scales are often inappropriate to describe the whole phenomenon and follow putative effects of therapies over time.

Second, chronic pain involves different neurotransmitters and neuronal circuitries at a spinal and supra-spinal level: therefore, non-invasive stimulation applied over a limited brain target usually induces a transient pain improvement.

Third, only few groups have enough experience about the use of neurophysiological tools for pain assessment [30]; among these techniques, laser evoked potentials (LEPs) offer an unique opportunity to study the sensory-discriminative, as well as the affective-emotional dimension of pain, which are differently carried by medial and lateral spinal nociceptive systems and rely on the activation of distinct cortical areas [31–33].
