Search

Allocentric spatial memory, “where” with respect to the surrounding environment, is one of the three fundamental components of episodic memory: what, where, when. Whereas basic allocentric spatial memory abilities are reliably observed in children after 2 years of age, coinciding with the offset of infantile amnesia, the resolution of allocentric spatial memory acquired over repeated trials improves from 2 to 4 years of age. Here, we first show that single-trial allocentric spatial memory performance improves in children from 3.5 to 7 years of age, during the typical period of childhood amnesia. Second, we show that large individual variation exists in children's performance at this age. Third, and most importantly, we show that improvements in single-trial allocentric spatial memory performance are due to an increasing ability to spatially and temporally separate locations and events. Such improvements in spatial and temporal processing abilities may contribute to the gradual offset of childhood amnesia.

L’étiologie des allodynies mécaniques est sujette à la controverse. Dans cette recherche, 25 allodynies mécaniques stastiques (AMS), traitées par rééducation sensitive (n = 23 patients), ont été étudiées topographiquement: les AMS cartographiées (allodynographies) rétrécissent en surface. Leur mode de disparition successif a été cartographié, ainsi que l’apparition de leur hypoesthésie. Le centre de la cartographie de la dernière AMS se situe en regard du centre de la dernière cartographie de son hypoesthésie (esthésiographie secondaire): 9,7 mm en moyenne ± ET = 8,0 (étendue: 1–38 mm). Nous concluons que l’AMS disparaît vers le centre de son hypoesthésie. En présence d’une hypersensibilité au toucher, cette observation devrait aider le clinicien à identifier l’étiologie du nerf cutané lésé., The aetiology of mechanical allodynia is still controversial. In the present study, we investigated the precise locations of 25 static mechanical allodynias (SMA) treated by somatosensory rehabilitation (n = 23 patients): the allodynic territory mapped (allodynography) was seen to shrink. The mode of progressive regression and finally disappearance of the SMA was mapped, as was the hypoaesthesia. The center of the final SMA map is aligned with the center of the final hypoaesthesia map (secondary aesthesiography): the inter-center distance was on average 9.7 mm ± SD = 8.0 (range: 1–38 mm). We conclude that the SMA disappears in the direction of the centre of the underlying hypoaesthesia. In cases of hypersensitivity to touch, this observation should help the physician identify the damaged cutaneous nerve.

Allocentric spatial memory, the memory for locations coded in relation to objects comprising our environment, is a fundamental component of episodic memory and is dependent on the integrity of the hippocampal formation in adulthood. Previous research from different laboratories reported that basic allocentric spatial memory abilities are reliably observed in children after 2 years of age. Based on work performed in monkeys and rats, we had proposed that the functional maturation of direct entorhinal cortex projections to the CA1 field of the hippocampus might underlie the emergence of basic allocentric spatial memory. We also proposed that the protracted development of the dentate gyrus and its projections to the CA3 field of the hippocampus might underlie the development of high-resolution allocentric spatial memory capacities, based on the essential contribution of these structures to the process known as pattern separation. Here, we present an experiment designed to assess the development of spatial pattern separation capacities and its impact on allocentric spatial memory performance in children from 18 to 48 months of age. We found that: (1) allocentric spatial memory performance improved with age, (2) as compared to younger children, a greater number of children older than 36 months advanced to the final stage requiring the highest degree of spatial resolution, and (3) children that failed at different stages exhibited difficulties in discriminating locations that required higher spatial resolution abilities. These results are consistent with the hypothesis that improvements in human spatial memory performance might be linked to improvements in pattern separation capacities.

Episodic memories for autobiographical events that happen in unique spatiotemporal contexts are central to defining who we are. Yet, before 2 years of age, children are unable to form or store episodic memories for recall later in life, a phenomenon known as infantile amnesia. Here, we studied the development of allocentric spatial memory, a fundamental component of episodic memory, in two versions of a real-world memory task requiring 18 month- to 5-year-old children to search for rewards hidden beneath cups distributed in an open-field arena. Whereas children 25–42-months-old were not capable of discriminating three reward locations among 18 possible locations in absence of local cues marking these locations, children older than 43 months found the reward locations reliably. These results support previous findings suggesting that allocentric spatial memory, if present, is only rudimentary in children under 3.5 years of age. However, when tested with only one reward location among four possible locations, children 25–39-months-old found the reward reliably in absence of local cues, whereas 18–23-month-olds did not. Our findings thus show that the ability to form a basic allocentric representation of the environment is present by 2 years of age, and its emergence coincides temporally with the offset of infantile amnesia. However, the ability of children to distinguish and remember closely related spatial locations improves from 2 to 3.5 years of age, a developmental period marked by persistent deficits in long-term episodic memory known as childhood amnesia. These findings support the hypothesis that the differential maturation of distinct hippocampal circuits contributes to the emergence of specific memory processes during early childhood.