last updated:

May 02, 2021

[Brain Image]    

PSY 340 Brain and Behavior

Class 36: Approaches to Classifying and Diagnosing Mental Disorders [OUTLINE]


Classifying Mental Disorders & Psychiatric Conditions: Conflicting Models
[Not in our text]

Dog ≠ Lion ≠ Wolf ≠

Dogs       are not       Lions       are not        Wolves       are not       Tigers

Each animal is a distinct and different type or species.

How about "mental disorders"?

Can we say "Depression" is not "Schizoprhenia" is not "Anxiety" is not "Substance Abuse"?

Are the "mental disorders" each a distinct and different type or species?

The study of pathological or abnormal mental and behavioral processes is known as psychopathology

A. The Need for Order => taxonomies.

Taxonony (taxis in Greek = ordering or arrangement of things; nomos = law, custom, how things are distributed or managed)

  • 1.Classification, esp. in relation to its general laws or principles; that department of science, or of a particular science or subject, which consists of or relates to classification; esp. the systematic classification of living organisms.
  • 2. A classification of something; a particular system of classification. (Oxford English Dictionary)

There are many different examples of taxonomies or classifications in science.

  • Red
                    Fox ClassificationBiology
    • Carl Linneaus & the binomial system: genus & species
      • Homo sapiens
      • Tyrannosaurus rex
    • Modern scientific classification of all living organisms has 8 levels in its taxonomy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, & Species
    • Most General to Most Specific
  • Zoology

A general presupposition in Biology and Zoology = "Nature can be carved at its joints" = the world is filled with "natural kinds"

  • The world is made up of distinct and different natural kinds of realities such as different species of animals, of plants, and other natural phenomena: a dog is not a lion is not a wolf is not a tiger.
  • When biologists and zoologists refer to different species, they are pointing to "natural kinds".

B. Sciences of Health and Disease => nosology.

Nosology  (nosos in Greek = disease; logos/logy in Greek = study of)

  • 1a. A treatise dealing with diseases; a classification or arrangement of diseases.
  • 1b. A list or catalogue of known diseases.
  • 1cc. A collection or combination of diseases 
  • 2.The systematic or scientific classification or investigation of diseases; the branch of medical science which deals with this. (Oxford English Dictionary)
Medical Nosology
  • How many illnesses, diseases or medical disorders are there in human beings? That number is very much disputed and under constant research.
  • Are there common elements or similarities that somehow link diseases together? These similarities may include
    • Symptoms
    • Causes
    • Course
    • Treatments
    • Prognosis

What are some of the general medical classification systems used today? There are two major ones which are most important

  • International Classification of Diseases (ICD; World Health Organization)
  • The Systematized Nomenclature of Medicine (SNOMED), originated in the US in the 1960s, became SNOMED-CT (CT = Clinical Terminology)

C. Classifying Mental Disorders

There are two general approaches to classifying what we call mental illnesses or mental disorders: (1) Categorical Approach and (2) Dimensional Approach

1. The Categorical Approach

  • Emil Kraepelin (1856-1926)
  • Syndrome = a collection of symptoms that are correlated and appear together in a medical disease. It is not the symptoms of themselves but the pattern of the symptoms appearing together that defines the syndrome.
  • Psychoses: dementia praecox (= "early madness" and renamed as "schizophrenia" (= "split in the mind") by Eugen Bleuler later on) and manic depression (now seen as a range of disorders including bipolar disorder and major depression).
  • Alois Alzheimer & Alzheimer's disease
  • Each mental disorder is basically a discrete or separate kind of "illness" (mental illness is a "disease") and that persons with these disorders function in ways that are different from how "normal" persons function. In the categorical approach, a person either has or doesn't have the illness or disorder.
Kraepelin   DSM-5
  • Diagnostic and Statistical Manual of Mental Disorders (DSM) (3rd edition, 1980) by the American Psychiatric Association
  • DSM-5, published in 2013
  • Criticisms of the DSM-5 have included a concern that (1) too many problems of ordinary life are now being labeled as a "mental disorder" and (2) the overall reliability of the criteria for these mental illness (that is, the consistency by doctors in agreeing on the same diagnosis) is still too low. 
2. The Dimensional Approach

The findings from genetics research (e.g., genome-wide association studies of specific disorders) suggest that there are wide overlaps among the various disorders.

Genetic Overlap

What else is wrong with the categorical approach?
  • Disorders are on a continuum
  • Low reliability (consistency) of diagnoses
  • Multiple forms of a disorder
  • Extensive co-morbidity
  • Overlooked patients
The "dimensional" approach holds that either
  • [1] each disorder lies at the end of a spectrum ranging from "normal" to "abnormal" and that the line dividing what is normal from what is abnormal is unclear, and/or
  • [2] each disorder is composed of a set of symptoms which are shared to varying degrees across different kinds of disorders
In the simple model cited by Adam (2013) below, five major psychiatric conditions are characterized by differing mixtures of four dimensions: cognition, negative symptoms, positive symptoms, and mood swings.
Dimensions of psychopathology

A different example: Autism. As Chung (2021) argues, "Genetic research has taught us that what we commonly call autism is actually a spectrum of hundreds of conditions that vary widely among adults and children.  Across this spectrum, individuals share core symptoms and challenges with social interaction, restricted interests and/or repetitive behaviors." (emphasis added)

The "family of disorders" approach (there is no commonly accepted name for this) argues that each different diagnostic label (e.g., schizophrenia, depression, anxiety) actually represents a set of multiple different disorders which may share certain symptoms in common. Thus the diagnostic label is a kind of "family name" for a collections of related but distinct disorders much like the general notions of "cancer" or "heart disease" (which are really multiple kinds of diseases).

The Hierarchical Taxonomy of Psychopathology (HiTOP): A Dimensional Alternative to Traditional Nosologies (Kotov, et al., 2017)