Differential Effects of Early Hippocampal Pathology on Episodic and Semantic Memory Vargha-Khadem et al Group B1!! Is… Mohamed Sharif, Brandon Thomas And Presenting Tonight: Meesha Sidhu and Marc Del Zotto

Some Background Declarative Memory – Episodic: Memory for events, placed specifically in time. Context-Rich variety. – Semantic: General world knowledge, facts, and, of course, meanings of words. Meesha Sidhu

What had been shown: Dissociation between Episodic/Semantic memories: – Previous patients lost Episodic but not Semantic Meesha Sidhu

But Question: Is semantic memory preserved because the existing base of knowledge helps by providing links for new information? OR… Do Semantic and Episodic memory systems operate effectively independently; do they use different neural machinery? Meesha Sidhu

How can we test this? Meesha Sidhu

Meet: Beth – Now 14 – Likely hypoxic brain injury, followed by seizures after birth. Jon – Now 19 – Born at 26 weeks gestation (14 weeks premature). Convulsions at age 4. Kate – Now 22 – Toxic dose of asthma medication at age 9, followed by seizures and respiratory arrest. Meesha Sidhu

Shared Symptoms Major memory deficits – Spatial – Temporal – Episodic Meesha Sidhu

Results of neuropsychological tests Meesha Sidhu

Recall Tests A – Story recall Immediate and 90 min delay B – Reproduction of Geometric Design Immediate and 40 min delay C – Word recall Immediate and 20 min delay Marc Del Zotto

Rey-Osterreith Complex Figure 3-5 min copying period 40 min delayed recall Marc Del Zotto

3D imaging Slices A – Normal individual image B – Amnesic patient image (Beth) Diffuse hippocampal atrophy Slice used for 1 H MRS analysis Marc Del Zotto

Hippocampal cross-sectional area Marc Del Zotto

Magnetic resonance data A – Hippocampal volumes Left and right hippocampi B – Hippocampal T2 values Left and right hippocampi C – MRS signal intensity ratios Left and right temporal lobes Marc Del Zotto

What does this mean? Episodic and Semantic memories were really spared to the same degree OR Context-Rich and Context- Free memory systems depend differentially on the Hippocampus and surrounding Cortical areas Two Possibilities: Marc Del Zotto

SO, how can we tell the difference? These three patients tested and compared to controls Only sig. differences shown were object-place and voice-face recognition Results similar to those obtained in non-human primates with hippocampal lesions and subjacent cortices left intact Look at Human and Non-Human Primate test results, and compare: Marc Del Zotto

This suggests: More specific rather than diffuse functionality of hippocampus and surrounding cortical areas. – Episodic (Context Rich; requires hippocampal processing) – Semantic (Context-Free; surrounding cortical areas are sufficient) Marc Del Zotto

Thanks for listening!