Thalamus & Amygdala

The Thalamus

Overview

The thalamus is heavily involved in relaying information between the cortex and brain stem and within different cortical structures. Because of this role in corticocortical interactions, the thalamus contributes to many processes in the brain including perception, attention, timing, and movement. It plays a central role in alertness and awareness.

Case study

The thalamus connects many different brain areas including the cortex and the cerebellum. A 2007 case study by Ro and colleagues highlights the importance of the thalamus to integrating information from these different areas. They examined a patient with a thalamic lesion that caused synesthesia. Synesthesia is the blending of sensory experiences, such that people may hear colors or see sounds. In this case, the patient reported a relatively rare form of synesthesia (tactile synesthesia) that caused the patient to “feel sounds.”

Associated functions

• relaying motor and sensory information
• memory
• alertness
• consciousness
• contributes to perception and cognition

Associated cognitive disorders

A number of neuroimaging studies show a small but significant reduction in thalamus volume in schizophrenia, which correlates deficits in language, motor, and executive processes (Corsica and colleagues, 2008). It has also been linked to many other cognitive disorders including bipolar disorder, ADHD, Alzheimer's, autism, and depression.

Associated with damage

• amnesia
• apathy
• coma
• dementia
• difficulty speaking (aphasia)
• loss of alertness and activation
• sleepiness
• impaired processing of sensory information
• inattention
• impaired movements and posture
• pain

Research reviews

• Stoelzel and colleagues (2009) examine firing rates and amplitude changes in thalamocortical synapses in alert and non–alert states (PMID: 19474312).
• Price and Drevets (2012)review animal and human studies and show dysfunction in the thalamus associated with major depressive disorder and bipolar disorder (PMID: 22197477).
• Dham and Alexander (2013) present a case study of a patient with bipolar disorder and a thalamic lesion (PMID: 23594838).
• Corsica and colleagues (2008) highlight an association between reduced volume in the thalamus and the onset of schizophrenia (PMID: 18570200).
• Sherman and Guillery (2011) distinguish the functions and role of transthalamic corticocortical pathways (PMID: 21676936).
• Carlesimo and colleagues (2011) review the literature on thalamic lesions and how they are associated with amnesia (PMID: 21255590).
• Ro and colleagues (2007)present a case study of a patient who developed auditory–tactile synesthesia after a thalamic lesion (PMID: 17893864).

Links

• Medical Subject Headings (MeSH)
• BrainInfo

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The Amygdala Overview The amygdala is a complex structure adjacent to the hippocampus. The amygdala is involved in processing emotions, and fear–learning. It links areas of the cortex that process “higher” cognitive information with hypothalamic and brainstem systems that control “lower” metabolic responses (e.g. touch, pain sensitivity, and respiration). This allows the amygdala to coordinate physiological responses based on cognitive information – the most well–known example being the fight–or–flight response. The amygdala has three functionally distinct parts – 1) the medial group of subnuclei has many connections with the olfactory bulb and olfactory cortex, 2) the basolateral group has extensive connections with the cerebral cortex, particularly the orbital and medial prefrontal cortex, and 3) the central and anterior group of nuclei has many connections with the brainstem hypothalamus, and sensory structures. Case study The neurological patient SM has extensive damage to the amygdala in each hemisphere. She has no motor, sensory, or cognitive deficits. When asked to identify photographs of a series of facial expressions, SM could identify every expression but one, she could not recognize fear. Similarly, when asked to draw facial expressions, SM produced accomplished pictures of each emotion, but she could not reproduce the expression of fear. When asked about her drawings, she explained that 'she did not know what an afraid face would look like.' Associated functions fear–processing emotion processing learning fight–or–flight response reward–processing Associated cognitive disorders Many studies have linked autism with amygdala dysfunction. The lack of empathy often shown by autistic individuals has associated with the amygdala (Blair, 2008). Neural activity in the amygdala has also been strongly linked to depression (Northoff, 2007) and bipolar disorder (Phillips&Vieta, 2007). There is very strong evidence linking post–traumatic stress disorder with amygdala responses (Brewin, 2008). Associated with damage aggression irritability loss of control of emotion disruption of short–term memory deficits in recognizing emotions (particularly fear) Research reviews Blair (2008) discusses two disorders, psychopathy and autism, in relation to abnormal amygdala functioning (PMID: 18038346). Brewin (2008) reviews neurological correlates of post–traumatic stress disorder, which has been strongly linked to the amygdala (PMID: 18037017). Phillips and Vieta (2007)consider functional abnormalities of the amygdala as potential biomarkers of bipolar disorder (PMID: 17562698). Morrison and Salzman (2010) review the different roles of the amygdala, including coordinating affective/emotional responses (PMID: 20299204). Northoff (2007) reviews the neuropathology of depression, which has been linked with abnormal neural activity in a number of structures, including the amygdala (PMID: 17379318). Roozendaal and colleagues (2009) review studies that found neural correlates of stress–induced modulation of the amygdala (PMID: 19469026). Crocker and colleagues (2013) review evidence for cognitive biases and deficits in depression and anxiety, and how they interact with emotional processes (PMID: 23781184). Links Medical Subject Headings (MeSH) BrainInfo