Cognition, depression and cognitive changes in Major Depressive Disorder: a brief consideration

Carolina received her Psychology, Clinical and Cognitive Neuroscience bachelors degree from Royal Holloway University of London and she has recently obtained a MSc degree in Translational Neuroscience from Imperial College London: Cognition is extremely fascinating. It is my belief that understanding how we learn is the key to self-actualisation.


Cognition is a term that refers to all the mental processes involved in the interpretation of the environment, including overt behaviours and emotional states, by mean of sensory experience (Neisser, 2014). For example, while watching a rugby match, we may interpret a physical contact between two players as being painful based on the visual information of a bleed and on the emotional reaction of a cry. The mental processes supporting the production of deliberate actions are also components of cognition (Neisser, 2014). Reaching for an object, for instance, would require focused attention to the target and online adjustments of the body position in the space relatively to the object.

Cognitive abilities are a determinant aspect of quality of human life. Reports suggest that cognitively skilled children obtain more prestigious occupations later in life (Cheng & Furnham, 2012) and a significant portion of variability in academic achievement in adulthood is explained by general cognitive ability (Rohde & Thomposon, 2007). In the elderly population, good cognitive functioning is associated with more satisfactory interpersonal relationships (Watanabe et al., 2016), engagement in social activities, hobbies, sports, volunteering, and generally more diversified daily activities (Fu et al., 2018).

Aging is accompanied by a cognitive deterioration that differently affects fluid and crystallised abilities (Cattell, 1943). The former comprise reasoning skills employed to solve mental operations and tasks (Murman, 2015), such as inferring the fastest bus route to approach a specific city district. Crystallised abilities constitute instead cumulative knowledge (i.e. facts) and experience acquired in the course of time (Murman, 2015). In 2009, a large cross-sectional study revealed that while fluid skills constantly deteriorate from late adolescence, crystallised abilities increment along with age, reaching a plateau in the 60s (Salthouse, 2009).

Cognition is, in part, genetically determined (Hill et al., 2014). However, a wide range of modifiable environmental factors can ‘accelerate’ or ‘attenuate’ cognitive decline. Interpersonal relationships contribute to maintain cognitive health by promoting social identification and support (Haslam et al., 2016). Furthermore, cognitive functioning is supported by higher levels of education, socioeconomic status and intellectual activity (Parisi et al., 2012). Nonetheless, various environmental risk factors can negatively affect cognition, such as smoking (Waisman Campos et al., 2016), a poor diet (Shatenstein et al., 2012) and low levels of physical activity (Kelly et al., 2014).

Cognitive functions can also be affected by depression. Major depressive disorder (MDD) is a common psychiatric disorder that negatively affects mood, thoughts and behaviours, compromising the ability to function both at work and at home. It is characterised by symptoms including low mood, loss of interest, fatigue, appetite changes, suicidal thoughts, difficulty thinking and irritability, for a period of time of at least 2 weeks (American Psychiatric Association, 2013). Major depression is one of the most disabling illnesses: it contributes to early mortality causing 60% of worldwide suicides (World Health Organization, 2009) and it has elevated annual pharmaceutical costs (Kessler, 2012), thus constituting a major global social and economic concern.

The onset of MDD typically occurs in late adolescence, and it is more prevalent among women than men (Hasin et al., 2018). It annually affects ~6.7% individuals, and ~16.6% of the population experience it at least once it in their life (Kessler et al., 2005). Importantly, depression not only represents a risk factor of accelerated cognitive decline, but it affects cognitive functioning in the everyday-life experience. Depressed individuals are more likely to ‘misinterpret’ neutral faces as expressing anger (Watters & Williams, 2011) compared to healthy controls. The ‘tendency’ towards negative emotions in depression is moreover accompanied by a lower ‘reactivity’ to positive stimuli, whereby hedonic pictures are considered to be less pleasant and less arousing compared to healthy subjects (Sloanab et al., 1997).

Furthermore, depression is generally linked to deficits of memory (Burt et al., 1995) including a decreased recognition and retrieval of previously learned words (Brand et al., 1992), visuomotor ability, such as a reduced horizontal eye-movements span (Deijen et al., 1993), but also mental flexibility (Airaksinen et al., 2004), language fluency (Reischies & Neu, 2000), abstract reasoning (Naismith et al., 2003) and decision-making, with an increased risk of impulsively engaging in pleasurable activities with harmful consequences (Chamberlain & Sahakian, 2006).

What is the impact of existent therapies on depression and cognition?

Recently, the effect of three different antidepressant drugs has been tested on patients with MDD and diminished functioning in seven cognitive domains including attention, verbal memory, mental flexibility, decision-making and information-processing (Shilyansky et al., 2016). The results showed that while all the antidepressants succeeded in improving mood-related symptoms, their effectiveness on cognition was limited to only two domains: mental flexibility and executive functions, namely organizing and planning skills. Talking treatments, such as the cognitive behavioural therapy, have been shown to improve the clinical symptoms of depression (Twomey et al., 2014), although their impact on cognitive dysfunctions are yet to be explored.

This is an exciting research avenue for the future: further investigations are required to delineate the distinct components of cognition, to elucidate the nature and extent of the cognitive changes in depression, as well as, to develop novel approaches to address specific deficits.


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