Attention and Inhibition in Older Adults

Question 1

What is attention?

Answer 1

• Top-down, goal oriented (endogenous) vs bottom-up, stimulus driven (exogenous)
• Distinction between focussing on what is relevant and ignoring what is irrelevant:
  1. Selective attention (towards a target)
  2. Inhibitory control (in relation to distractors)

Question 2

What are the regions supporting attention?

Answer 2

• Dorsal and ventral attention networks
• These networks are largely considered to be separate but also overlap

1. Dorsal:
   - Top down control
   - Intraparietal sulcus (IPS)
   - Superior parietal lobule (SPL)
   - Frontal eye fields (FEF)
2. Vental:
   - Detection of relevant stimuli/filtering
   - Temporoparietal junction (TPJ)
   - Inferior frontal gyrus (IFG)
   - Medial frontal gyrus (mFG)

Question 3

Structures supporting attention: Superior Longitudinal Fasciculus (SLF)

Answer 3

• Fibres of the SLF connect dorsal frontoparietal areas and also ventral frontoparietal regions e.g. v1PFC to IPL, d1PFC to SPL
• They also connect the parietal component of the ventral network with the prefrontal component of the dorsal network, allowing communication between the two systems
• Where white matter integrity is seen to decline across the lifespan, the distributed frontoparietal attention network is particularly vulnerable, due to the long-range connections that support it

Question 4

Events supporting attention

Answer 4

• Frontoparietal ERPs
• P1/N1: basic stimulus processing but sensitive to task demands, which influence amplitude
• P2/N2: higher order perceptual processing. Detects mismatched stimuli, relies on prior knowledge and expectation. N2pc as an index of successful orienting towards a target
• P3: Separate components in relation to distractors (P3a) and targers (P3b)

Question 5

Frontal eye fields and ageing

Answer 5

• The FEFs play a crucial role in sustained attention. TMS to this region induces poor accuracy and reaction time variability
• FEF exerts top-down modulation on visual attention. TMS-fMRI shows BOLD signal in higher-order visual regions, related to target features, is altered with TMS to right FEF
• FEF also appears to re-orient attention due to deficits in the suppression of irrelevant information
• Better performance with increased FEF activity (for older, not younger participants)
• In temporal judgement task, lower levels of occipital beta-band activity correlated with decreased behavioural performance - predicted to originate from poor FEF activity

Question 6

Intraparietal sulcus and ageing

Answer 6

• tDCS to anterior IPS improves multiple object tracking, particularly at high loads
• Functional connectivity between dorsal (IPS) and ventral (TPJ) networks is still present in later life but the ventral network does not sufficiently deactivate in older participants when task demands are high
• MEG data show that high-gamma power in the left IPS is correlated with individual processing sped, showing a specific impairment in non-target processing. Additionally, older adults peak frequency was considerably lower than that of young adults

Question 7

IFG/mFG and ageing

Answer 7

• Key role in processing task-relevant stimuli: Older adults who exhibited higher high-gamma power in the left mFG exhibited fast and accurate responses to the target
• Older adults are less able to modify mFG response to higher stimulus load, meaning performance suffers
• Reactive vs proactive inhibition
  _ Cures related to stopping behaviour produce decreased activation of the rIFG
• Clear age-effect on proactive inhibition: rather than flexibly engaging the rIFG, older subjects showed an overall hyperactivation

Question 8

TPJ and ageing

Answer 8

• Debate over ‘circuit breaker’ role of TPJ in over-riding the dorsal network and re-orienting attention: role in P3b generation, which occurs post-perception
• Good functional connectivity of the ventral/salience network in ageing, including the TPJ
• However, TPJ activity reflects greater attention capture from irrelevant stimuli in older adults. Working harder at lower levels of demand across the lifespan e.g. moving from states of rest to basic tasks

Question 9

How does age affect attention?

Answer 9

• Aspects of selective, sustained, and divided attention all decline with age, as well as the ability to switch between tasks
• Task difficulty is a major factor in performance
• Comparison of task performance under varied inhibition loads shows a breakdown in attention mechanisms as the demand for resources increases
• Age related activity in PFC goes up a with low and medium loads, but goes down when demand for resources is high

Question 10

Reasons for age-related attention change: reduced sensory-specific processing

Answer 10

• Declines in primary sensory regions (visual, auditory, cortex etc) make it harder to search for and detect stimuli with the same precision as in youth

Question 11

Reasons for age-related attention change: Reduced top-down inhibition

Answer 11

• Attention cannot be directed efficiently to modify selection, irrelevant items are not ignored and are processed alongside target information

Question 12

Support for bottom up deficits

Answer 12

• Dedifferentiation as a key contributor to age-related change
• Less functional specialisation of dorsal and ventral attention networks in ageing (Grady et al., 1992)
• PET scans show that activity to object and space based tasks is not as distinct, suggesting declines in bottom-up processing across the lifespan
• Large/slow occipital N1 with increasing task difficulty (Wang et al., 2012)
• Deficits in low-level processing with higher attentional demands