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.
Highlights
Memory impairment is a frequent symptom of depression, it is not a cardinal criterion for diagnosis [1]
We searched for olfactory differences between unipolar and bipolar depression that may be considered as differentiation markers, with possible consequences for the therapeutic approach to these two forms of depression
Our results showed that olfactory recognition memory is altered in both unipolar and bipolar depression patients compared to healthy individuals
Summary
Memory impairment is a frequent symptom of depression, it is not a cardinal criterion for diagnosis [1]. Disorder (MDD) present memory problems that affect their daily functioning [2]. It is not clear if memory symptoms persist or disappear after symptomatic remission of depression. According to DSM-5 (Diagnostic and Statistical Manual for Mental Disorders—5th edition), in successfully treated depressed patients, memory symptoms may fully abate after remission [1]. Subjects suffering from depression present memory biases in the form of preferential recall of negative information [3]. Liu et al. Changes in olfactory recognition memory may constitute sensory markers in 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. Results: DU, DB, and EU patients had a deficit in olfactory memory compared to HC
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