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Reflection Of The Limbic Function

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The Limbic System
The limbic system refers to a collection of subcortical structures in the brain that surround the thalamus. Among other structures, this area consists of the amygdala, olfactory cortex, hippocampus and parahippocampal gyrus in the medial temporal lobe. Individuals with medial temporal lobe amnesia have shown impairment for learning as well as retrograde amnesia for recent events, but no such deficit for remembering remote events (Bayley, Hopkins, & Squire, 2003; Reed & Squire, 1998).

The Limbic Function in Olfaction
Odourants bind to the olfactory receptors in the back of the nasal cavity, sending sensory information to the glomeruli in the olfactory bulb. This signal is relayed through the olfactory nerve to the primary olfactory cortex (piriform) in the medial temporal lobe, classically considered to be part of the limbic system. This is a primitive area of the brain associated with the processing of emotion and memory (Shipley and Ennis 1996; Haberly and Price 1977; Carmichael et al. 1994). Olfactory information is also processed in the orbito-frontal cortex (OFC) in the forebrain where odours are consciously identified. For both of these modalities however, no evidence was found of thalamic relay to both the primary olfactory cortex and the OFC. This is in contrast with other sensory systems in the brain, normally relaying information through the thalamus in the midbrain before being processed in the cortex. Olfaction is the only mode of sensation that completely bypasses this area of the brain (Sullivan & Mouly 2010). As a result, olfaction is inferred to be more directly related to other limbic processes involving emotions and memory (Sullivan, Wilson & Mouly, 2015).

There has been substantial evidence to support this claim, fMRI studies have found piriform, amygdalar and hippocampal activation to be evident with olfactory stimulation (Herz et al., 2004; Poellinger et al., 2001). A study by Herz & Cupchik (1995) found that odour-evoked autobiographical memories of paintings with emotionally positive and negative valence were enhanced when the odour and valence of the paintings were hedonically congruent. Activation was also found in the hippocampus and parahippocampal area. However,

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