Impairments in precision, rather than spatial strategy, characterize performance on the virtual Morris Water Maze: A case study

Abstract

Damage to the medial temporal lobes produces profound amnesia, greatly impairing the ability of patients to learn about new associations and events. While studies in rodents suggest a strong link between damage to the hippocampus and the ability to navigate using distal landmarks in a spatial environment, the connection between navigation and memory in humans remains less clear. Past studies on human navigation have provided mixed findings about whether patients with damage to the medial temporal lobes can successfully acquire and navigate new spatial environments, possibly due, in part, to issues related to patient demographics and characterization of medial temporal lobe damage. Here, we report findings from a young, high functioning patient who suffered severe medial temporal lobe damage. Although the patient is densely amnestic, her ability to acquire and utilize new, but coarse, spatial “maps” appears largely intact. Specifically, a novel computational analysis focused on the precision of her spatial search revealed a significant deficit in spatial precision rather than spatial search strategy. These findings argue that an intact hippocampus in humans is not necessary for representing multiple external landmarks during spatial navigation of new environments. We suggest instead that the human hippocampus may store and represent complex high-resolution bindings of features in the environment as part of a larger role in perception, memory, and navigation.

A network approach for modulating memory processes via direct and indirect brain stimulation: Toward a causal approach for the neural basis of memory

“…Suthana et al (2012) showed improvements in navigation performance following acute stimulation of the entorhinal cortex, with their specific measure being the accuracy with which patients navigated to a goal location store (termed excess path length, i.e., Newman et al, 2007). Because navigation is often associated with integrity of the hippocampus (i.e., Astur, Taylor, Mamelak, Philpott, & Sutherland, 2002;Kolarik et al 2016;Morris & Garrud, 1982) and not of the entorhinal cortex (e.g., Hales et al, 2014), the authors attributed the effects of stimulation to entorhinal cortex as occurring because it resulted in more endogenous, regularized input into the hippocampus than direct stimulation of the hippocampus (Suthana et al, 2012). In support of this argument, direct stimulation of the hippocampus had no effect on navigation yet stimulation of entorhinal cortex did reset on-going low frequency oscillations in the hippocampus.…”

Evidencing a place for the hippocampus within the core scene processing network

“…Beyond the seminal work in both rats and non‐human primates—which identified HC cells attuned to allocentric location [O'Keefe and Nadel, 1978] and spatial view [Rolls, 1999]—recent models of human medial temporal lobe (MTL) function highlight the HC as an important structure for scene processing, via a proposed role in representing complex and conjunctive scene stimuli [Graham et al, 2010; Lee et al, 2012; Murray et al, 2007] and/or by contributions to viewpoint‐independent scene construction [Bird and Burgess, 2008; Maguire and Mullally, 2013; Zeidman et al, 2015]. These complex HC scene representations have been shown to support behavioural performance across a range of cognitive domains, including recognition memory [Bird et al, 2008; Taylor et al, 2007], short‐term memory [Hannula et al, 2006; Hartley et al, 2007], working memory [Lee and Rudebeck, 2010a, 2010b; Park et al, 2003], perceptual learning [Mundy et al, 2013], higher‐order perception [Aly et al, 2013; Barense et al, 2005, 2010; Kolarik et al, 2016; Lee et al, 2005b] and scene imagination [Hassabis et al, 2007]. …”

Memoria espacial de largo plazo en humanos entrenados en un laberinto virtual

“…El resultado tiene un rango de 0 a 1, e indica la zona donde preferentemente se buscó la plataforma: un IP > .5 refleja una mayor búsqueda en el subcuadrante interno (es decir, mayor precisión); un IP < .5 refleja mayor búsqueda en la zona periférica del cuadrante reforzado (es decir, menor precisión); y un IP = .5 refleja que la búsqueda es indistinta entre estas dos áreas. Su uso atiende a la necesidad de evaluar la precisión en la conducta de búsqueda en tareas espaciales más que la permanencia en zonas específicas (Kolarik et al, 2016).…”

“…De forma parecida a lo reportado en otros estudios (Astur, Purton, Zaniewski, Cimadevilla & Markus, 2016;Kolarik et al, 2016), estas variables se consideraron como un indicador del nivel motivacional de los participantes durante la prueba. El indicador 1 se empleó en la fase de entre-namiento, mientras que el 2, el 3 y el 5 se utilizaron en ambas pruebas, y el 4 solo en el postest.…”

“…Posteriormente, durante un ensayo de prueba sin plataforma, los sujetos muestran típicamente una preferencia por el área en que esta se localizó. En general, en roedores los ensayos de entrenamiento se distribuyen en diversas sesiones diarias y la prueba se realiza después del ensayo final o tras un IR de 24 h (Morris, 1984;Vorhees & Williams, 2014), mientras que en humanos se realiza tanto el entrenamiento como la prueba en una sola sesión (Astur, Ortiz & Sutherland, 1998;Goodrich-Hunsaker et al, 2009;Hamilton, Driscoll & Sutherland, 2002;Jacobs et al, 1997;Kolarik et al, 2016;Schoenfeld et al, 2014).…”