Table 1.

Summary of aging studies

Brain Region	Neuron Type	Species	Gender	Dendritic Regression	Spine Density	Cognitive Decline	Reference
PFC	pyramidal	Mouse	male	~45% decrease in apical length; preservation of complexity			(Shimada et al., 2006)
PFC	pyramidal	Macaque monkey		25% reduction of apical dendrites; decrease in complexity	43% decrease on proximal apical dendrites; 27% loss in basal dendrites		(Duan et al., 2003)
PFC		Rhesus monkey			25% loss of spines		(Cupp and Uemura 1980)
PFC	pyramidal	Rhesus monkey			33% loss of spines, with a 50% loss of thin spines; 32% decrease in axospinous synapses	impaired performance on the DNMS task	(Dumitriu et al., 2010)
Hippocampus (DG)		Rat			reduction in axospinous and perforated synapses	impaired in hippocampus-dependent spatial memory tasks	(Geinisman et al. 1986, 1992)
Hippocampus (OML of DG)		Rhesus monkey			reduction in perforated synapses	impaired performance on the DNMS task	(Hara et al., 2011)
Hippocampus (MML of DG; stratum radiatum of CA1)		Rat	male		no change in synapse densities		(Shi et al., 2007; Newton et al., 2008)
Hippocampus (stratum radiatum in CA1)	pyramidal	Rat	male	regression of apical dendrites; decrease in complexity	no change in spine density, in either sex		(Markham et al., 2005)
			female	No change in neuronal complexity
Hippocampus (CA3)		Rat			24% decrease in synapses		(De Groot and Bierman, 1987)
Hippocampus (CA3, stratum lacunosum-moleculare)		Rat	male		decrease in macular axospinous synapses; no change in size		(Adams et al., 2010)
Cerebellum	Purkinje	Rat		retraction of dendritic arbors; atrophy of soma			(Chen and Hillman, 1999) (Graham and van Ooyen, 2006)
Cerebellum	Purkinje cells	Rat	male		33% loss in axospinous synapses		(Glick et al., 1979)
Cerebellum	Purkinje cells	Rat	male	dendritic regression, especially distal	17% lower spine density		(Rogers et al., 1984)
Striatum (caudate)	medium-sized spiny	Cat		~40% decrease in total dendrite length and mean branch length	40% loss of distal spines; higher proportion of ‘enlarged-head’ spines		(Levine et al., 1986)
Striatum; Hypothalamus		Rat	male		axospinous synapses fewer in number, but with greater mean area		(Itzev et al., 2001, 2003)
Substantia Nigra	Types I, II, III	Human		Distorted cell body; varicosities in and loss of dendrites	Types I-II: severe spine loss; remaining spines thinner and longer		(Cruz-Sanchez et al., 1995)
Amygdala	bitufted and multipolar	Rat	male		spine density unchanged with age		(Marcuzzo et al., 2007)
Amygdala	principal neurons	Rat		increased dendritic arborization	spine density unchanged with age		(Rubinow et al., 2009)