Pathological mental health problems in children and young adults have been classified into externalizing (substance abuse, conduct disorder etc) and internalizing disorders (depression , anxiety etc). Today’s post will try to  work out the structure of this internalizing spectrum.

The first major difference, that is made in say DSM, is between Mood disorders (disturbance in mood) and Anxiety disorders (characterized by anxiety and avoidance behaviors) . However, Watson in this article (pdf) emphasizes that this classification is not proper and in many cases these disorder say depression (say MDD) and Anxiety (say Panic disorder) are co-morbid with each other.

To explain this as well as other genotypical and phenotypical findings, Watson has developed a structure of these ‘distress disorders’ – however the road was long, an intermediate stop was tripartite model of depression/anxiety.

According to this tripartite model (developed by Watson and Clark), both depression (MDD, dysthymia etc)  and anxiety disorders (phobia, panic etc) share a common non-specific factor called Negative Affect (NA) which is characterized by things like preponderance of negative emotions like sadness, fear, guilt, anger etc as well as irritability, difficulty concentrating etc.

Depressive disorders meanwhile are specifically characterized by lack of Positive Affect (PA), which means less emotions like happiness, interest etc, but also Anhedonia or inability to derive pleasure from earlier pleasurable experiences.  Anxiety disorders, on the other hand, are characterized by physiological hyper arousal (PH) (shortness of breath, dizzyness etc) .

This model however was also found wanting and replaced with an hierarchical integrative model, which posited that there was a generic non-specific factor of NA common to both anxiety and depressive disorders, and a lower order low PA factor characterizing depression and more specific multiple low order factors (instead of one PH hyperarousal factor) associated with the different types of anxiety disorders like panic/ agoraphobia, Phobia-specif stimuli, phobia social etc .

However , Watson further modified the structure and came up with this model shown below:   One broad factor of distress/NA; two specific factors of anxious-misery and fear and then further unique factor specific to individual diagnosis.

To summarize and also extending it a a bit,

1. At top there is an internalizing spectrum and associated with it a non-specific NA factor.
2. In middle there are four spectrum:-  a depressive spectrum , a Fear spectrum and a bipolar spectrum and an Obsessive compulsive spectrum.
3. each of these can be further divided into discrete diagnosis along two factors/dimensions (I will not eb focusing too much on bipolar or OCD for the purposes of this post) :
   1. Depressive spectrum :
      1. group 1: MDD and dysthemia
      2. group 2: GAD and PTSD
   2. Fear Sepctrum
      1. group 1: Panic and agarophobia
      2. group 2: Phobia (specific stimuli) and Social Phobia
   3. Bipolar spectrum (bipolar I, II and cyclothymia)
   4. OCD

Lets focus more closely on Depressive and Fear Spectrum and try to see alignment with ABCD model. MDD/Dysthemia imho are mainly about mood or Affect;  GAD/PTSD are more Cognitive (reaming stuck in a thought loop) ; Panic/agorophobia more Physiological or Dynamic in nature and Phobia (both specific and Social) more Behavioral in nature (avoiding people, places and animals).

Each of these in turn splits into four factors; for ex PTSD splits into four factors- Dysphoria (A), Intrusions (C), Hyperarousal(D) and Avoidance (B). Similarly, recent research has shown that MDD is itself heterogeneous made up of four neural subtypes- one way to list those would be – marked primarily by Anhedonia (A), Anxiety (C) , Psychomotor retardation (D) and Fatigue (B) . Similar analysis should be possible for other discrete diagnosis.

For now, we will turn to the structure of Bipolar and OCD spectrum by analogy to dep/anxiety spectrum.

1. Biploar spectrum:
   1. Euphoria (Affective)
   2. Flight of ideas (Cognitive)
2. OCD spectrum
   1. Obsessions (Dynamic)
   2. Compulsions (Behavioural)

Within this OCD can be seen to be comprising  of four factors: Hoarding (A?) , Order and symmetry (C), Obsessions and Checking (D) and Washing and cleaning (B).

Another way to think about the depressive and anxiety spectrum is to say that Depression rgoup 1 is characterized by Low PA, depression group 2 by high PH; Fear group 1 by High PH and Fear group 2 by low PA. What distinguished Fear spectrum from Depression spectrum is the fact that much more variance is explained by High NA for depressive syndromes and only moderate variance explained by NA for Fear syndromes.

What do you think is missing from the above model? Where might it be wrong? where might it be correct? If correct what are the implications?