Olfactory Memory in Depression: State and Trait Differences between Bipolar and Unipolar Disorders

Abstract

Background: Changes in olfactory recognition memory may constitute sensory markers in depression. Significant differences may exist between unipolar and bipolar depression. Our study compares olfactory memory between control, unipolar, and bipolar patients in depressed and euthymic states in order to identify potential markers of depression. Methods: 176 participants were recruited in 5 groups: depressed bipolar (DB), euthymic bipolar (EB), depressed unipolar (DU), euthymic unipolar (EU), and controls (HC). The participants had a standardized clinical and olfactory assessment (olfactory memory, evaluation of pleasantness, intensity, familiarity, and emotional aspect of smells). Results: DU, DB, and EU patients had a deficit in olfactory memory compared to HC. DB patients had lower capacity to recognize new odors. DB and DU patients had more limited detection of unfamiliar odors than HC. DB patients rated odors as less pleasant compared to the other groups. All groups had lower hedonic ratings than HC. DB patients had lower emotional ratings than EU patients. Conclusions: Olfactory memory is impaired in depressive states, thus constituting a state marker of depression. Impairments in olfactory memory persist after remission of bipolar depression, thus constituting a possible trait marker of bipolarity. Hedonic rating differentiates unipolar from bipolar depression. This is the first study that identifies a sensory marker differentiating between unipolar and bipolar depression.

Odour identification impairment is a trait but not a disease-specific marker for bipolar disorders: Comparisons of bipolar disorder with different episodes, major depressive disorder and schizophrenia

“…In Experiment 2, we compared OI and OS between patients with BD, MDD and SCZ and found impaired olfactory function in all patient groups, with SCZ patients showing the worst performance in both olfactory function tests, except normal OS in euthymic BD patients. The lack of differences in olfactory function between depressed BD and MDD patients is in accordance with previous reports (Kamath et al, 2018; Kazour et al, 2020; Swiecicki et al, 2009). Recent imaging studies indicate that compared to BD, SCZ patients show a greater reduction in grey matter volume in the frontal-temporal cortex, hippocampus and amygdala (Maggioni et al, 2016; Nenadic et al, 2015), which are involved in olfactory processing.…”

Is abnormal metabolism in the olfactory bulb and amygdala associated with bipolar disorder?

“…A study on smell recognition in patients with BD and major depression reported that patients with BD depressive episodes and unipolar depression had a greater odor loss compared to control groups. This decreased olfactorious recognition memory persists in euthymic bipolar patients after remission of the depressive episode (Kazour et al 2020 ). Lahera et al reported that the deficiency in odor identification in patients with the euthymic period of BD was permanent and related to permanent cognitive impairment of BD patients in remission (Lahera et al 2016 ).…”

Olfaction as a Marker for Dystonia: Background, Current State and Directions

“…A (disease) marker is either a substance, a measurable parameter, or a physical sign of a disease [ 178 , 179 , 180 , 181 ]. There are two types of markers: trait markers and state markers.…”