The following alterations were reported: (i) poor native nest building behavior in young (3 mo) and old (9 and 20 mo) PrPC knockout mice; (ii) higher latency in exploring a new environment only in young but not in old PrPC knockout mice; (iii) more pronounced drop in anxiety during aging in PrPC knockout mice; (iv) decline in associative learning in old PrPC knockout mice compared to age-matched wild-type. This evidence concerns the gene PRNP and Anxiety.