Descriptive Psychopathology: The Signs and Symptoms of ...

69 Chapter 3: The brain and psychopathologyThe cerebellum has several cognitive as well as motor functions. 79 Posteriorand lateral regions (primarily cerebellar neocortex) are relevant for cognition.Vermus lesions are associated with changes in emotional expression.The cerebellar neocortex has direct reciprocal interaction with the contralateralprefrontal cortex via cortico-pontine and cortico-olivary projections, and byconnections through the lateral thalamic nuclei. Cerebellar neocortex volumecorrelates positively with performance on tests of non-verbal reasoning in normalpersons. 80 Right cerebellar cortex lesions can elicit left frontal deactivation,producing a fluctuating aphasic syndrome characterized by expressive and receptiveagrammatisms. 81 Focal cerebellar lesions are associated with deficits inexecutive functioning, attention, and working memory. 82 The cerebellum alsoplays a role in word search and its dysfunction is associated with the paucity ofspeech seen in many patients with schizophrenia. 83The cerebellum acts in preparatory processes via altering cerebral blood flow orby differential enhancing of neural responsiveness of targeted brain areas (particularlythe contralateral frontal circuitry) in the performance of a wide range ofcognitive tasks. In cerebellar disease the ability to perform these tasks is not lost,but efficiency and coordination among tasks is diminished. This is termeddysmetria of thought.The cerebellum has substantial afferent and efferent connections to the midbrainand limbic system and is also involved in emotional regulation and inmovements associated with emotional expression. Cerebellar function, throughthe thalamus, integrates with prefrontal circuits in a variety of processes includingmotivation and emotional expression. 84Cerebellar vermus connections to the thalamus are ipsilateral. 85 In addition tocoordination, the cerebellum modulates temporal–limbic activity, motor planning(trial and error learning of skills), new learning of procedural sequences(e.g. sports, dance steps), and speech and language (organizing some languageelements and speech sound motor sequences).The thalamus and cerebellum receive input from the brainstem, and thethalamus is the terminus for the reticular activating system. The thalamus isthe lynchpin of the motor system. It links the sensory and motor systems,transfers cerebellar input to the frontal cortices, provides tone to the frontallobes from the reticular activating system, receives input from the basal gangliaforming the circuits of specific frontal cortices, and connects to the limbicsystem, accounting in part for the association between strong emotion andmotor behavior. Thalamic lesions are also associated with stupor and apathy.Morphologic changes in the thalamus have also been reported in patientswith schizophrenia. 86