A new neural framework for visuospatial processing

Group #4

Alicia Iafonaro Alyona Koneva

Barbara KimIsaac Del Rio

Monkeys Humans

Functional evidence from PCC in Monkeys Dean, H. L. & Platt, M. L. (2006)

• Experiment designed to assess egocentric vs. allocentric coding in PCC

• Results show the neurons in PCC encoded visual stimulus in both egocentric and allocentric locations, even when monkey’s head position rotated. Monkeys did show bias towards allocentric coding.

• So, monkeys know where they are in relation to their environment, and they know an object in the environment doesn’t necessarily move just because they do.

• Conclusion: Posterior Cingulate Cortex provides spatial information to the Medial Temporal Lobe.

Functional evidence from Humans with damage to RSC

Hashimoto, R., Tanaka, Y. & Nakano, I. (2010)

• Experiment with RSC damaged humans designed to determine ability to coordinate allocentric and egocentric representations.

• Change in orientations of subjects significantly affected their recall of object locations, after changes in egocentric position.

• This shows that the RSC is crucial for updating spatial representations after changes in heading.

Functions of the Posterior Cingulate Cortex

• In monkeys:– The PCC is connected with the supplemental eye field– PCC neurons are strongly modulated by the onset of behaviorally

relevant targets, saccades made to those targets, and the motivational value of them.

– PCC neurons encode locations of eye movements and their targets in allocentric coordinates.

– PCC contributes to the translation between the egocentric representations of space in the posterior parietal cortex and the allocentric representations in the MTL.

– Inactivation of the PCC neurons can lead to deficits in following previously learned routes.

The functional properties of the PCC include eye movements (saccades), attention, and navigation.

• In humans:– Activated during eye movement tasks and participates in shifting

spatial attention.– Responds during top-down shifts of attention in response to cues.– Correlates with the speed of target detection and increase in that

speed for cued targets – suggesting its role in the allocation of visual attention throughout a display in response cues.

– Active when moving dots simulate optic flow of a type that would be consistent with the observer moving forward along an unknown direction.

Functions of the Posterior Cingulate Cortex Continued…

Functional properties of the MTL

•MTL and the hippocampus are the most studied parts of the brain in primates. •Hippocampus becomes active during topographic learning and navigation. Parahippocampal place area (PPA)-in humans responsible for retrieving landmarks and objects relevant to navigation. PPA is sensitive to spatial layout of objects and responds to topographic and spatial learning.

Posterior parahippocampal cortex (PPC) +Perirhinal and entorhinal cortices = PPA

When the PPA (which is the human homologue of the monkey areas TFO, TF and TH) is damaged it leads to:• Landmark agnosia: people can orient themselves in their environment, and even make maps, but they cannot understand prominent and important landmarks necessary to navigate. •Anterograde topographic disorientation, which means that individuals can navigate to places they are familiar with, but they can’t store information about new locations.

The Retrosplenial Cortex (RSC)• The RSC is involved in spatial memory,

imagination, and planning• Serves as a “connectional hub” for the posterior

parietal cortex, posterior parahippocampal cortex, and the hippocampus

And more importantly…• The RSC may play a role in the coordination of

egocentric heading and allocentric representations of the environment

Lesions of the RSC•RSC lesions in humans lead to heading disorientation (topographical disorientation) which is a cognitive disorder were patients are unable to orient themselves in respect to landmarks in the environment. •To better understand this, here is a case study of a person with a damaged RSC

A 55 year old cab driver for 10 years, suddenly lost his knowledge of the route to is home. He could recognize buildings and knew where he was. However, he could not use those buildings to remember the route to his house. He had a hemorrhage in his left RSC.

Dudchenko, P. A. (2010). Why people get lost: the psychology and neuroscience of spatial cognition. New York: Oxford University Press.