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Concept cells: the building blocks of declarative memory functions
Rodrigo Quian Quiroga
Abstract | Intracranial recordings in subjects suffering from intractable epilepsy made during their evaluation for an eventual surgical removal of the epileptic focus have allowed the extraordinary opportunity to study the firing of multiple single neurons in awake and behaving human subjects. These studies have shown that neurons in the human medial temporal lobe respond in a remarkably selective and abstract manner to particular persons or objects, such as Jennifer Aniston, Luke Skywalker or the Tower of Pisa. These neurons have been named Jennifer Aniston neurons or, more recently, concept cells. I argue that the sparse, explicit and abstract representation of these neurons is crucial for memory functions, such as the creation of associations and the transition between related concepts that leads to episodic memories and the flow of consciousness.
More than 2,000years ago, Aristotle argued that our thoughts are based on internal representations of the external world, and he distinguished between sensation (the image impinging on the retina) and perception (the interpretation we give to the stimulus)1.
Nowadays this view constitutes one of the most basic principles of brain function.
The sight of a familiar person or the sound of this persons voice, for example, triggersa cascade of brain processes that creates a representation leading to the recognition of the person, the recollection of details related to him or her and the generation of new memories.
The study of how neural populations give rise to such exquisite processes has been a subject of active research for decades. In particular, a large number of studieshave established that neurons in the ventral visual pathway (FIG.1) are involved in visual recognition25. Along the ventral visual pathway there is an increase of selectivity to complex features and visual invariance25:
neurons in V1 (the first cortical visual processing area) represent the minute details that compose an image, whereas neurons in the inferotemporal cortex respond toa high-level representation of the image.
From the inferotemporal cortex there are massive projections to the medial temporal lobe (MTL)68. Evidence from animal studies911, patient H.M.1215 and other patients with lesions in the hippocampus and theMTL11,16,17 have clearly demonstratedthe key role of the MTL...