4) Key questions

Question 1

What is semantic dementia?

Answer 1

• Semantic dementia is a progressive neurodegenerative disorder characterised by:
  1. Gradual loss of semantic memory.
  2. Preserved cognitive functions such as phonology, syntax, working memory, and visuo-spatial abilities.
  3. Fluent speech that lacks content and meaning.
  4. Atrophy mainly in the anterior temporal lobes (ATL), especially the inferior-lateral temporal neocortex.
• Patients may say things like “I like doing things” when asked about hobbies, or not understand words like “hobby”.

Question 2

What are category-specific disorders of semantic memory? Name a theoretical account of this impairment.

Answer 2

• Category-specific disorders involve selective impairments in recognising or naming certain types of concepts (e.g., animals vs. tools)
  1. Some patients show impairment for living things e.g., animals, plants), others for non-living things (e.g., tools, vehicles).
  2. Evidence includes studies of semantic dementia, stroke, and herpes simplex encephalitis.
• One key theoretical account: Sensory/Functional Theory (Warrington & Shallice, 1984)
  1. Living things rely more on sensory properties (e.g., what they look/sound like).
  2. Non-living things rely more on functional knowledge (e.g., what they’re used for).
• Damage to one system = selective category impairment.

Question 3

What is a ‘semantic hub’

Answer 3

• A semantic hub is a proposed amodal integration centre in the brain where information from different modality-specific regions (the “spokes”) is brought together to form conceptual knowledge.
• The anterior temporal lobe (ATL) acts as this hub.
• Damage to the hub (e.g., in SD) leads to generalised semantic impairment across all categories and modalities.
• The “hub-and-spoke” model supports this:
  1. Hub = ATL, integrating all knowledge.
  2. Spokes = visual, auditory, motor ect representation.

Question 4

What is a temporal gradient, and why is it important in comparative theoretical discussions of semantic and episodic memory impairment?

Answer 4

• A temporal gradient refers to the pattern where older memories are more preserved than newer ones, typically seen in retrograde amnesia.
• Important in theory:
  1. Consolidation Theory (Squire, 1992): All types of declarative memory (episodic and semantic) follow a time-based consolidation showing a temporal gradient.
  2. Multiple Trace Theory (MTT) (Moscovitch et al., 1998): only semantic memory shows a temporal gradient. episodic memory remains dependent on the hippocampus throughout life, so no gradient.
• Semantic dementia patients often show a. reverse temporal gradient - more recent facts about themselves are better preserved.