A Neuroscientist’s Framework of Neuropsychologically-Relevant Disorders

This framework is organised by the primary cognitive or behavioural domain that is disrupted, linking it to the typical brain regions involved and example conditions.

Category 1: Disorders of Memory (The Amnesias)

These disorders involve the failure to encode, consolidate, or retrieve information.

• Amnestic Syndrome: Characterized by a profound anterograde amnesia (inability to form new memories) and often retrograde amnesia (loss of memories prior to the injury).

  • Brain Regions: The medial temporal lobe system, especially the hippocampus, and the diencephalon (mammillary bodies, thalamus).

  • Exemplary Conditions:

    • Alzheimer’s Disease (early and prominent feature).

    • Korsakoff’s Syndrome (from thiamine deficiency, often due to alcoholism).

    • Post-encephalitis or hypoxic brain injury (oxygen deprivation).

    • Herpes Simplex Encephalitis (can severely damage the temporal lobes).

• Other Memory Disturbances:

  • Semantic Dementia: A progressive loss of conceptual knowledge (facts, object meanings) with relative preservation of episodic memory. Linked to degeneration of the anterior temporal lobes.

Category 2: Disorders of Language (The Aphasias)

These are acquired disorders of language processing, not of the motor act of speaking.

• Non-fluent Aphasia (Broca’s): Labored, agrammatical speech with relatively preserved comprehension.

  • Brain Region: Broca’s area (posterior inferior frontal gyrus) and surrounding regions.

• Fluent Aphasia (Wernicke’s): Fluent but meaningless speech, with severe impairments in comprehension.

  • Brain Region: Wernicke’s area (posterior superior temporal gyrus).

• Global Aphasia: A severe impairment of all language functions.

  • Brain Region: Large perisylvian lesions encompassing both Broca’s and Wernicke’s areas.

• Primary Progressive Aphasia (PPA): A neurodegenerative syndrome where language is the primary and initial deficit.

Category 3: Disorders of Executive Function

These involve deficits in higher-order cognitive control: planning, problem-solving, inhibition, and mental flexibility.

• Dysexecutive Syndrome: Includes poor planning, impulsivity, disinhibition, inflexible thinking, and impaired judgment.

  • Brain Region: The prefrontal cortex, particularly the dorsolateral (planning, working memory) and orbitofrontal (inhibition, social behaviour) regions.

  • Exemplary Conditions:

    • Frontotemporal Dementia (bvFTD – behavioural variant).

    • Traumatic Brain Injury (TBI), especially frontal lobe contusions.

    • Prefrontal tumours or strokes.

    • Advanced Hydrocephalus.

Category 4: Disorders of Visuospatial and Perceptual Processing (Agnosias)

The inability to recognise objects, faces, or spatial relationships, despite intact basic sensation.

• Visual Agnosia: The inability to recognise visually presented objects.

  • Brain Region: The occipito-temporal visual “what” pathway.

• Prosopagnosia: The specific inability to recognise familiar faces.

  • Brain Region: The fusiform face area (in the temporal lobe).

• Simultanagnosia: The inability to perceive more than one object at a time. A key feature of Bálint’s syndrome.

  • Brain Region: Bilateral damage to the parieto-occipital junctions.

Category 5: Disorders of Body Awareness and Representation

• Anosognosia: A lack of awareness or denial of one’s own neurological deficit (e.g., a paralysed patient insisting they can move their arm).

  • Brain Region: Typically the right inferior parietal lobe or right frontal-parietal networks.

• Hemineglect: A failure to attend to, or represent, the side of space contralateral to a brain lesion (most commonly the left side after a right hemisphere stroke).

  • Brain Region: The right inferior parietal lobe, temporo-parietal junction, and superior temporal gyrus.

Category 6: Disorders of Social Cognition and Emotion

• Behavioral Variant Frontotemporal Dementia (bvFTD): Presents with early and profound changes in personality, social conduct, and empathy, often with disinhibition and loss of moral judgment.

  • Brain Region: Atrophy in the frontal and anterior temporal lobes, particularly areas like the ventromedial prefrontal cortex.

• Autism Spectrum Disorder (ASD): Characterised by challenges in social interaction, communication, and theory of mind (the ability to attribute mental states to others).

  • Brain Regions: Involves complex network-level differences, including the amygdala, temporo-parietal junction, and prefrontal regions.

Category 7: Syndromes from Disconnection

These occur when white matter tracts connecting specialised brain regions are severed.

• Alexia without Agraphia: The inability to read, while writing and other language functions remain intact. Caused by a disconnection between the visual cortex and the language areas.

  • Brain Lesion: Damage to the left primary visual cortex and the splenium of the corpus callosum.

The Neuroscientist’s Conclusion

From a neuropsychological perspective, the goal is not just to name a disease, but to:

1. Profile the Cognitive Deficit: Precisely characterise the impaired and spared functions using standardised tests.

2. Localize the Dysfunction: Link the cognitive profile to a specific brain network or region.

3. Inform Diagnosis and Rehabilitation: Use this understanding to differentiate between conditions (e.g., Alzheimer’s vs. FTD) and to design targeted cognitive rehabilitation strategies.

Therefore, this framework is a map of the mind’s functional geography. A “neuropsychological disease” is essentially a lesion on this map, revealing the intricate and specialised organisation of the human brain. This is a far more powerful concept than a simple list.