A deficit in familiarity-driven recognition in a right-sided mediodorsal thalamic lesion patient

According to a still-controversial view of recognition, projections between the perirhinal cortex and the medial subdivision of the mediodorsal thalamic nucleus (mMDT) support the mnemonic processes underlying familiarity, whereas a separate extended hippocampal system is critical for the recollection of episodic details during recognition.

In this study, we examined item recognition, familiarity, and recollection for faces and words in a patient (OG) with a right-sided lesion centered on the mMDT, which encroached on the central medial midline nucleus and may have resulted in partial disconnection of the mammillothalamic tract. On the basis of OG's neuropathology, the dual-process signal-detection (DPSD) high-threshold theory and the material-specific hypothesis of long-term memory together predicted a material-specific impairment in familiarity for novel facial memoranda, with a lesser decline in recollection of novel faces at short retention intervals. No abnormalities in either familiarity- or recollection-driven recognition of verbal memoranda were expected.

Comparing the performance of OG and that of a group of 10 age-, sex-, and IQ-matched healthy controls, the remember-know procedure revealed the dissociations predicted by the material-specific and DPSD hypotheses: With recognition of previously novel faces, OG showed a deficit in familiarity-driven recognition that was significantly greater than the insignificant reduction in his recollection. All components of his word recognition were, however, preserved.

A memory profile, marked by a dissociation between familiarity and recollection, fits naturally with the DPSD model and is incompatible with the idea that these kinds of memories reflect different degrees of trace strength.