## 3 Cerebellum and Emotional Processing  
### Cerebellar Involvement in the Unconscious Component of Emotions  
Cerebellar function in emotional responses at the unconscious level is supported by its influence on the modulation of autonomic reactions and the automatic components of emotional learning. Based on clinical observations in patients affected by cerebellar damage, there is a lowered skin conduction response to negative stimuli [14] and an impaired blink reflex to fear stimuli [74]. Reports of impaired responsiveness of arterial blood pressure to aversive stimuli in animals [87] and a less extensive increase in heart rate during fear conditioning tasks in subjects with vermal lesions [75] indicate that the cerebellum is also involved in the autonomic neural pathways that subserve the cardiovascular system in emotion regulation [87; 88; 89]. Furthermore, fMRI studies have implicated that the cerebellar vermis is involved in autonomic responses that are associated with fear conditioning [78; 89; 80; 83]. Fear is a crucial emotion and the capacity to develop fear-related memories has an important evolutionary advantage. The regulation of fear and fear memories consists of motor/autonomic components (changes in blood pressure and heart rate, dilation of pupils), endocrine, behavioral responses (freezing behavior, potentiated startle reflex) [90], and the affective component. It has been proposed that the cerebellar vermis mediates the conditioning of fear-related changes in autonomic functions, even in the absence of contingency awareness [91; 90; 92]. The central autonomic nuclei in the brainstem and cerebellum control the sympathetic and parasympathetic axes of the autonomic nervous system, allowing for the production of integrated somatic response patterns that are necessary for the metabolic support of emotional behavior [78]. The cerebellum is an important component in the central autonomic network [93], because the vermis is connected to the brainstem (catecholamine neurons) and hypothalamus [60]. Furthermore, the vermis is connected with limbic areas--such as the amygdala, hippocampus [90], periaqueductal gray [94; 95], and sensory cortices [96; 97]--which function in emotional learning during fear conditioning and generate the appropriate emotional behavior patterns [94; 95]. Taking into account these connections, the vermis can be viewed as the interface between the sensory stimuli, emotional state, and motor responses of a subject. Thus, in the vermis, learning-related plasticity might be crucial for relaying the appropriate emotional and motor behaviors in response to sensory stimuli and maintaining this information for long periods. Consistent with this hypothesis, various animal studies have shown that the potentiation of excitatory [98; 99] and inhibitory [100] synapses that impinge on the same Purkinje cells correlates with associative fear learning. These changes at the cellular level have long-lasting effects and are related to associative processes. Other data support cerebellar function in the unconscious components of emotional processes with regards to its involvement in the implicit processing of facial expression [37]. [PERSON] et al. [37] found that repetitive Transcranial Magnetic Stimulation (rTMS) over the midline cerebellum enhances the implicit processing of happy facial expressions, with no changes in consciously experienced mood. These findings have been explained by projections from the cerebellar vermis to the ventral tegmental area of the midbrain, thus modulating the mesolimbic areas through ventral tegmental dopaminergic projections [60] (see Table 1 for details on reported studies). These data from various experimental approaches suggest that the cerebellum automatically modulates emotional behavior to remain within homeostatic baseline levels and according to the context.