Interactions Between Attentional Networks and Their Influence on Perception
Condition: Hemispatial Neglect
MeSH terms: Perceptual Disorders
Study type: Interventional

Summary: 
      Attention can be defined as the preparedness to rapidly and accurately respond to stimuli
      coming from the investigators environment and to effectively select between relevant and
      irrelevant information. According to a current model, visual attentional control is based on
      two separate groups of brain regions, so called brain networks. These networks control
      different attentional aspects (e.g., spatial/non-spatial attention) and they interact with
      each other. A disruption of these interactions can lead to attentional disorders such as
      hemispatial neglect. Patients with hemispatial neglect have difficulties directing their
      attention to the left visual field and they act as though the latter does not exist.

      To date, the interactions between the two attentional networks are poorly understood. The aim
      of this study consists in further clarifying different aspects of these interactions and
      their influence on visual perception in healthy participants and in patients with hemispatial
      neglect. Transcranial magnetic stimulation (TMS) will be the principal method applied in this
      study. TMS is a painless and non-invasive method, with which the activity of brain areas can
      be influenced temporarily. This allows us to draw conclusions regarding the functions and
      interactions of these brain areas.

      This study is designed to have a significant impact on the basic understanding of attentional
      control in the human brain and it can benefit the comprehension and treatment of attentional
      disorders, such as hemispatial neglect.
    

Detailed description: 
      Background

      Attention can be defined as the preparedness to rapidly and accurately respond to stimuli
      coming from the investigators environment and to effectively select between relevant and
      irrelevant information. Attention is a complex cognitive function based on multiple
      components. A recent model postulates that attentional control in the brain is based on two
      discrete neural networks. The ventral (temporo-parietal - ventral frontal) network controls
      non-spatial aspects of attention, such as alertness and vigilance, and stimulus detection and
      reorientation in both hemifields. This network is lateralized towards the right hemisphere
      and plays a role as a 'circuit-breaker'. The dorsal (superior parietal - dorsal frontal)
      network controls spatial attentional shifts, is largely top-down driven, and substantially
      overlaps with eye movement control. This network is not functionally lateralized, each
      hemisphere containing dynamic topographical maps of the contralateral space. Moreover, the
      dorsal networks of the two hemispheres compete to direct attention to the contralateral
      hemispace, thereby exerting reciprocal inhibition.

      Hemispatial neglect - the failure to detect, orient, or respond to stimuli located in the
      contralesional side of space - has been interpreted in terms of pathological changes in the
      interaction between the two attentional networks. Neglect is very common after cerebral
      lesions of the right hemisphere, usually affecting the ventral attentional network. The
      structurally intact right dorsal network would thus receive a weakened input from the right
      ventral network. The ensuing imbalance in the inhibition between the dorsal networks of the
      two hemispheres would then result in the rightward bias in attentional allocation, typically
      observed in hemispatial neglect.

      However, little is known regarding the interactions between ventral and dorsal attentional
      networks and their influence on perception, and the greatest part of the evidence has been
      acquired through correlational approaches. The aim of this study is to further elucidate
      different aspects of these interactions and to investigate their influence on spatial and
      non-spatial attentional performance and on visual perception.

      Objective

      A first objective consists in further elucidating how and through which anatomical structures
      the ventral and the dorsal attentional networks interact. A second objective concerns how the
      interplay of dorsal and ventral attentional networks influences visual perception, in
      particular in cases in which visual stimuli are ambiguous.

      Methods

      Transcranial magnetic stimulation (TMS) is the principal method applied in this study. TMS is
      a non-invasive, painless method which is able to influence cortical areas directing attention
      in an interference approach and to thus establish causal relationships. Furthermore, TMS, in
      combination with the measurement of motor evoked potentials (MEP), allows for the assessment
      of the excitability of cortico-cortical circuits.
    

Intervention name(s): Transcranial magnetic stimulation (TMS); Sham coil stimulation; Control without stimulation
Intervention type(s): Device; Device; Other
Intervention description(s): This method will be applied to measure cortical excitability and as an interference approach; real TMS stimulation will be compared with sham stimulation and no stimulation; Stimulation with a sham coil as a comparison
Intervention model: Single Group Assignment
Masking: Single (Participant)
Primary purpose: Basic Science