The aspect of structural connectivity in relation to age-related gait performance

Fernandez et al. ( 2019 ). investigated the relationship between age-r elated c hanges in attention control and gait performance in older adults . T he study aimed to establish a more precise link between the influence of age on brain systems mediating executive cognitive functions and their relationship with gait disturbances. Ev ent-r elated functional ma gnetic r esonance ima ging (fMRI) data wer e acquir ed fr om 20 individuals (21 ± 3 years) and 34 older adults (72 ± 5 years) with no history of neur ological, psyc hiatric, or toxicological diseases to e v aluate a ge-r elated effects on the activation of the executive control brain network during a selective attention task. The study compared brain activation patterns be-tw een y oung and older participants with fMRI, and examined an association between a ge-r elated differ ences in activ ation patterns and gait par ameters, cognitiv e abilities, and physical abilities. The study demonstrated a greater sensitivity to attention interference and heightened recruitment of cortical executive control systems in elderly individuals with poor gate performance . T hese findings were associated with selective increases in gait variability indices . T he older participants exhibited differential recruitment of the left dorsal parieto-occipital sulcus and pr ecuneus, whic h wer e significantl y corr elated with higher gait


Neuroplasticity
The ability to mak e adapti ve changes related to the structural and function of the nervous system, known as neuroplasticity, has become an important aspect of neuroscience (May, 2011 ).Numerous clinical and neuroscience studies have provided substantial evidence to support neuroplasticity.
Rehabilitation has enhanced the brain function of adult stroke patients (over 18 years old) who experienced disability following a cer ebr ov ascular e v ent, pr omoting structur al c hanges in both gr ay matter (motor areas) and white matter (Gauthier et al., 2008 ;Diao et al., 2017 ).The group (av er a ge a ge 44 ± 15 years) that r eceiv ed 12 weeks of balance training sho w ed a significant impr ov ement in balance performance, along with an increase in cortical thickness in v arious br ain r egions associated with visual and v estibular self-motion perception (Rogge et al., 2018 ).Another study (av er a ge age 68 ± 6 years) also demonstrated improved memory performance, accompanied by an increase in the size of the hippocam-pus after 1 year of aerobic exercise (Erickson et al., 2011 ).The adult gr oup (av er a ge a ge 63 ± 4 y ears) that underw ent 12 w eeks of cognitiv e tr aining r e v ealed impr ov ed connectivity in the centr al executive network and increased white matter integrity in the left uncinate fasciculus (Chapman et al., 2015 ).Training focused on attention resulted in increases in cortical thickness in prefrontal regions, socio-affectiv e tr aining induced incr eases in fr ontoinsular r egions, and socio-cognitiv e tr aining alter ed inferior fr ontal and later al tempor al cortices in adults (av er a ge a ge 41 ± 9 years) who r eceiv ed mental training for 9 months (Valk et al., 2017 ).
The studies all highlight that the brain continues to change e v en in adulthood.Although no all-inclusive theory spans differ ent fr ame works in the study of neur oplasticity, ther e ar e two important biological hypotheses to explain it: functional plasticity and structural plasticity.Functional plasticity describes the br ain's ca pability to execute diverse functions or cooperate with other brain regions to compensate for various functions (Demarin et al., 2014 ).Inter estingl y, structur al c hanges in the br ain, known as structural plasticity, also occur to modify its organization or patterns of connectivity (Butz et al., 2009 ).
Fernandez et al. pr ecisel y inv estigated the association between age and gait variability using task-based fMRI in terms of functional plasticity.We hypothesized that there would be age-related differ ences in structur al str ength within the executiv e contr ol network, pr oviding e vidence for the functional c hanges observ ed in the study.

Tr actogr aphy
Diffusion tensor imaging takes anisotropic features of water molecule diffusion within white matter fibers .T his imaging modality ca ptur es tensor information, whic h is subsequentl y utilized to compute eigenvectors and eigenvalues to represent the c har acteristics of the ellipsoid shape of the fibers (Assaf and P asternak, 2008 ).Eigenv ectors and eigenv alues ar e a pplied to estimate local fiber orientations and tr ace str eamlines, a tec hnique known as tr actogr a phy.(Nucifor a et al., 2007 ;Pal et al., 2012 ).Tr actogr a phy can be generated based on deterministic and pr obabilistic a ppr oac hes.Deterministic tr actogr a phy does not calculate uncertainty during the fiber orientation estimation process and is r elativ el y fast.On the other hand, probabilistic tractogr a phy takes uncertainty into account, but it r equir es mor e computational calculations compared to deterministic tractogr a phy (Sarwar, 2019 ).The indices obtained from tractography include the number of streamlines and tract volume.Tractography has been linked to structural connectivity and functional changes (Assaf, 2019 ;Zhang et al., 2022 ).
In patients with multiple sclerosis, working memory impairment and a decrease in the number of fiber connections were observed (Audoin et al., 2007 ).Quantitative analysis using tractography demonstrated that musicians exhibit heightened motor coordination, as evidenced by increased track volume and the number of streamlines in the superior and middle cerebellar peduncles compared to controls (Snell, 2001 ;Abdul-Kareem et al., 2011 ).Patients with COVID-19 demonstrated a significant association between olfactory dysfunction and reduced integration as well as incr eased segr egation in olfactory-r elated br ain r egions .T hese findings provide insights into compensatory plasticity mechanisms (Bispo et al., 2023 ).
There is a potential challenge in tr actogr a phy.Str eamlines in tr actogr a phy ar e constructed based on their likelihood, and errors can occur during the fiber tr ac king pr ocess (Jeurissen et al., 2019 ).Ho w e v er, it r emains v aluable for inv estigating r elationships between structural and functional changes in the brain using tractogr a phy.

Conclusion
This study r e vie wed the e vidence for neur oplasticity and intr oduced the feasibility of using tr actogr a phy in r elating br ain plasticity.From the perspective of structural plasticity, we anticipate that older adults may exhibit smaller tr ac k volume or fewer streamlines than younger individuals in the executive control networks and compensatory r egions suc h as the precuneus and dorsal parieto-occipital cortices as observed in Fernandez et al.'s study.These findings would enhance the reliability of the research and provide additional supporting evidence for the functional changes.